recently; PlayStation network has re-released Armored Core: Last Raven onto the PsP (or it isn't recent I cant usually tell the difference) and i Decided to pick up this game because i remember my brother playing Armored Core and it was freaking awesome. I never really got into these because the control map is insane, but i thought "if it works; it works." and it does
the only thing that I can see as an offset is that the game starts off pitting you at a choice between 2 factions: Vertex and the Alliance. Although this may seem bad; both factions try and make you fight a high-ranking Armored Core in the first few missions. You can import data from previous installments but don't expect that to save you; they're still pretty damn tough.
The AC (Armored Core) that you pilot is comprised of: a Head, Core, Arms, Legs, Booster, Radiator, Engine, which can all be fine-tuned to your specifications. On each arm, and the shoulder, you can attach a weapon. Weapon types vary from: Riles, Machine Guns, Lazar Blades, Shotguns, Grenade Launchers, Pulse Rifles, and even Shields, for people who want just a little more defense.
I don't know if this was in the previous games, but Armored Core: Last Raven, has a touranent-style arena where you bet XXXXX credits and go into battle with a ranking AC opponent. the victor walks out with money and the loser... well, you're out a lot of money.
and the whole damn thing can be painted this plethora of options makes for a good while of tuning, painting, and maximizing your AC's different capabilities.
Personally; i highly reccommend this game, due to the fact that it is indeed a very good Armored Core installment