All the tips so far seem to focus on the player classes. That's all well and good, but the only way to really be successful is to experiment with the classes for yourself. What my tips will focus on are the enemies.
Reapers:
General: Reaper forces have a combination of sustained fire troops and close range attckers ranging from swarmers, dealing minimal annoying damage, to brutes and banshees, dealing high damage and one hit kills. Reaper forces are designed to keep you in cover while their powerful melee units flank you, Their primary means of doing this is by covering your position with a wall of fire, their high damage ranged attacks discourage you from leaving cover, leaving you vulnerable to brutes and banshees. Conversely, on lower levels they use wek, but annoying melee units to force you OUT of cover and into the line of fire, often forcing a dramatic shift in player tactics. The Reapers forces encourage the use of cover on lower levels, by sending primarily ranged attackers, once brutes and banshees arrive players are forced to employ tactics almost entirely counter to those they had previously employed.
Husks: Their slender frame and waving movement make these weak enemies surprisinglyhard to hit with precision weaponry so semi-automatic and automatic weapons are advised. Husks are quite weak and anyone who has played Mass Effect is WELL accustomed to facing them. A new twist in thehusks' arsenal is their aility to both leap over cover and to latch on to the players dealing constant damage until killed by hammering melee or having a team mate remove them. They can also receive armour plating from Marauders. Much like Mass Effect 2 the legs of a husk are much weaker than the rest of the body, often being destroyed before the husk loses all it's heatlth, this kills the husk instanly. A husk's legs are also the only part which does not recieve armour plating.
Cannibals: The primary cannon fodder for the Reaper forces, Cannibals are mutated husks of Batarians with a human husk mounted as an arm cannon. Cannibals do not have very high health, though though their ranged attack is quite powerful and can take unaware players by surprise. Cannibals do not tend to move up to melee range, often prefering to stay back and lay down supressing fire. Canibals are usually the first units to receive armour plating and can consume dead husks to grant this buff to themselves. It should be noted that Cannibals become much more aggressive when armoured and often move in groups. It can be difficult to land a headshot on a Cannibal as their head is located in the center of the body mass, as opposed to the top.
Ravagers: Long range enemies with a nasty surprise inside. The Ravager's main attack is very powerful, able to take down a player in a single volley, even on Bronze. Care should be taken when fighting Ravagers as they can be quite powerful up close and at a distance. Their heavy armour allows Ravagers to soak up a lot of damage, and their incubation sacks carry a small swarm of swarmers, making them quite deadly up close. Shooting a Ravager's sacks not only releases the swarmers inside, but it also deals no damage to the swarmer itself. When possible avoid shooting the sacks. On a final note: Ravagers can even be lethal after death, their corpses quickly liquify into an acidic substance capable of tearing shields and barriers apart.
Swarmers: A single swarmer is not a threat, the swarmer deals minimal damage and is destroyed in it's own attack. A swarmer's real threat comes from it's geat numbers and miniture size. Often overlooked in the heat of battle a swarm of these tiny pests can quickly remove your shields and sap your health resulting in an unexpected demise. The best method of dealing with swarmers is to simply never allow them to spawn, killing the Ravagers which host them without breaking open their incubation sacks. Failing this it is recomended that you use automatic weapons to erradicate thses pests before they close in on yourself, or your team.
Marauders: A Marauder has powerful shields and decent health making it a threat on it's own. However Ravagers often imbue husks and cannibals with armour plating, whcih blocks all damage until the plating has been knocked off. When a wave begins Marauders should be your priority targets as their high shields, Phaeston assault rifles, and ally buffing abilities can often turn a mild threat into an overwhelming force.
Brutes: We all know 'em, we all hate 'em. Big SOBs with armour plating and a surprising reach. Wee al know to shoot for the head. But did you know that you can knock a brute's armour plating off, just like a cannibal or husk? You did, very well, well how about the fact that the brutes have a weak point in the back, the exposed and glowing spine deals similar damage to a headshot. Now your brute killing is more efficient, handy for silver and gold, no?
Banshees: Their slender frame and slow, menacing walk may give you the impression that behind the Banshee's powerful barriers is a soft target, easily subdued. This is not the case, the Banshee is easily the most poweful and formidable of the Reaper forces. Capable of instantly killing any player in melee range this devastating force will often cause teams of hardened soldiers to become disorganised. The Banshee has the most powerful barriers in the game, capable of withstanding long periods of sustained fire and recharging extremely quickly. It is advised that you focus on removing a Banshee threat as soon as possible and, if necessary, using a Cobra missile launcher. The Banshee's barriers are vulnerable to traditional barrier busting techiques, such as Concussive Shot and warp ammo. Shield draining technology, such as disruptor ammo and overload are also quite useful. The most important thing to remember when facing a Banshee is to not panic, a coordinated group can take down a Banshee with miniml trouble as it's powerful barriers can not withhold against sustained combined arms fire. Though players are warned to remember the Banshee's massive armour rating and rapid regeneration. Only a powerful and focused effort can reliably take down a Banshee. The Banshee also has an array of biotic attacks, from it's biotic area attack to it's powerful warp field, making this foe difficult to confront at close range. The Banshee can sometimes be stunned by attacking it as it uses it's biotic charge ability, though this is unreliable at best.[/i]
Cerberus:
General: Cerberus are often considered the easiest foe to fight. Despite their heavy use mixed unit tactics, flanking and heavy armour support Cerberus have the distinct disadvantage of being human, and therefore are predictable. Cerberus troops try to minimise their losses with covering fire, smoke and shielding. Troopers will usually try to flank and supress rather than push through or overwhelm.
Troopers: Cerberus troopers are the most easily countered foe in the game. While they have moderate attacking and defence capabilities they are only aggressive in the most predictable ways. The trooper is only willing to lay down his life when accompanied by a superior officer, often spending extended periods in cover waiting for an opening. They are prone to flanking, and will often try to find indirect route to their targets. Cerberus troopers do have a preference for grenades, throwing a seemingly limitless number behind the cover of entrenched players, though most players note this more as a minor annoyancethan a major threat.
Centurion: The Cerberus command unit, this enemy employs a mobile shield generator and smoke grenades. Centurions do not flank all that often, prefering to keep players occupied by laying down covering fire and heavy smoke screens. It should be noted the Centurions will only deploy smoke in choke points or on their squad, making their use slightly predictable. Certain scope upgrades for sniper rifles allow players to see enemies through this smoke, negating it's effectiveness. The Javelin sniper rifle has this property as a core function, rather than a modification.
Guardians: The Ceberus Guardian is armed with a Hornet SMG or a Paladin pistol, making them fairly powerful offensively. However the Guardian's real strength is it's thick shield. The shiled takes advantage of the mass driver weapons' design of flattening a round on impact, meaning while modern firearms are powerful against flesh a simple metal plate is enough to stop a shot dead. Firing on a Guardian's shield is both a waste of time and thermal clips. Precision shots from a sniper rifle or pistol are the optimal method of dealing with Guardians, by eaither shooting threw the view port or attacking the user's arms or feet. Flanking also works.
Combat Engineer: The Cerberus Combat Engineer has low health, high shileds and a weak weapon. Alone it is hardly a threat. However Engineers set up sentry turrets which are both incredibly powerful and deadly accurate. Engineers tend to stay out of direct combat, fucusing instead on repairing turrets and the formidable Atlas mechs. Using Sabotage to hack a Turret is often the easiest, as well as the funniest, ways of eliminating a Cerberus Engineer. You can also destroy the turret while it it on the engineer's back or as he sets itup to instantly destroy both.
Nemesis: A Nemesis has no close range combat abilities at all. As such it tends to stay as far way from players as possible. If approached it will simply try to run away. It has moderate shielding and low health, but compensates with massive damage. A nemeis often strips a players shields in a single shot. It is worth noting that the Nemesis uses the Rptor sniper rifle, one of the weakest but fastest firing sniper rifles availalbe, however the Nemesis uses it as a powerful single shot weapon.
Atlases: Atli? Atlasus? The Cerberus mechs. Anywho, we all know that sadly you can not hijack an Atlas in multiplayer but the glass is still a weak point, well worth focusing your fire. Did you know that the glowing eezo core on the back of an Atlas is actually it's weakest point? It's true! But wait there's more! Despite it's high armour rating and powerful weaponry the Altas is actually surprisingly unstable. So much so that a krogan charge can potentially stagger it, this tactic has a heavy risk, but the priiiize. Also biotic powers such as pull or throw can also stagger Atluses, though they deal minimal damage.
Phantoms: No one likes Phantoms, they have that hand-gun thing that instantly drains your barriers and EVERYONE has stories of how a single unchecked Phantom has ganked an entire team. However, did you know that Phantoms and Nemesises, I don't know Latin, often work in pairs? If you see a Nemesis lining up a shot be careful, a Phantom could be flanking you. Despite their speed, tactical movement and powerful barriers Phantoms have one major flaw the Phantom is actually one of the weakest enemies in the game, meaning once it's barrier is down it is pretty much screwed. They are particularly weak to stasis, headshots and sustained fire. If you are having trouble with Phantoms, and are ludicrusly skilled with a rifle you can actually shoot the sword out of a Phantom's hand, removing it's melee attacks entirely Though such a shot is incredibly hard to pull off and extraordinarily rare.
