Alright, I've always wanted to say my opinion of the Call of Duty series, so buckle up, because this will probably be a long read. TL;DR is at the bottom.
Since the start of the Call of Duty franchise, I never payed it much attention. The World War 2 story had been told to death, and I wasn't about to consider playing another shooter in the same era. It was only until Modern Warfare came around that I really cared.
I played Modern Warfare on my very old PC at the time, and it looked... pretty horrifying, but it ran and I didn't care. I sunk my teeth into the single player, and I was met with some rather intense gameplay. For one, the protagonist wasn't American, which was what really absorbed me into Soap's campaign. It was something I had wanted in a shooter for ages, a chance of pace and character. It was a good campaign, albeit really really short. Then, I sank my teeth into the multiplayer, which didn't work out as well. The loading times were fairly crap so I ended up joining maps a minute or two after they started. It was all fine though, but in terms of challenges and unlocks, it was nicely balanced. Not too many, not too few, and it was fairly fast paced, but not overbearing.
Then World at War came out.
This was the second CoD game I had bought. I went into this expecting too much. The singleplayer was... playable, but it failed to hold any emotional significance like Modern Warfare had done so neatly. It felt bland. It felt like everything had to be worked towards. Work you way up the beach, work your way up to the bunkers, work your way up to the building, work work work! And the multiplayer didn't hold up too great either! If you're not a fan of killing zombies, all that was left was co-op through uninspiring single player levels, or multiplayer which was comprised of more challenges, but with weapons that felt... meh. They felt boring, and underpowered. Sure you had a flamethrower, but just because it was violent doesn't mean it was fun. It was just one of those niche weapons you had to use every second mission. The perks also felt too bloated, like there were too many to choose from, with too many filling niches that you would have to be psychic to know when to use.
World at War came and went, and then we had Modern Warfare 2. This was one of the first games I bought with my PS3, and still the one that still gets some play time from me. The levels were varied and well designed with fun in mind. I'll admit, I played the first two missions with a bit of a worried look. It did feel a bit crap to start, as I had flashbacks of the rather linear parts and standoffs from World at War. That quickly disappeared once I got out of the school however. The game lived off the dramatic and often varied scenarios it threw you. From stealth operations, to shooting a crowd of civilians in an airport terminal. It wanted the player to be switching between different, very varied emotional states at once. World at War felt like "Yeah, lets burn some japs!" (I apologize if that's offensive, but that's what I felt World at War conveyed), compared to Modern Warfare 2's "Oh dear god! I have to... I'm going to have to... Oh jesus christ!" and it wanted you to be saying Oh Shit! the entire time! The multiplayer this time around boasted a good few improvements to the multiplayer. Challenge numbers were increased dramatically, but you felt rewarded for completing them, just to hear that metal riff play when you did! The weapons were expansive, possibly too expansive, but it was great to choose what you wanted with so many play styles. The maps are great, all of which focus on a set piece and have varied gameplay (The crashed plane in Afghan is a great example, as you could hide inside it, and interact with it). All the maps had this, and it made each and every one individual.
And my opinion of Black Ops, seeing as there's a free multiplayer weekend on? (I wrote this somewhere else, so I just copy-pasted it over)
I'm after downloading the thing, and it's taken me all of an hour to realize it is terrible! The maps are horrid and have no flow whatsoever. Routes commonly end up at a dead end, or with only one direction to go. Most of them are cramped corridors, or are so open there's no cover. The setpieces are missing which makes maps very hard to focus on. All the colours are washed out, so it really gives that brown'n'bloom feeling way too much. I'll admit MW2 had this a bit as well, but it still varied those shades of brown.
The weapons sound like cap guns. There's no power in them, no recoil, most of them feel like they were modeled on plastic toys. The perks are unimaginative and boring, some even being direct copy and pastes from previous games, and some being direct copy and pastes while taking some of the original functionality away! Killstreaks are bland, and what sounds awesome at first (attack dogs) end up being really cheap and not very fun for the victim.
Finally, all sense of accomplishment is gone as you buy your equipment through CodPoints which you earn through play. They're fairly easy to acquire, but the only gating towards buying anything is a level limit. And it's only ever used on weapons. Once you have the weapon, you can buy all the attachments straight off. It's not fun, It's not rewarding, and it's not pleasant to look at.
So, why do I hate Call of Duty and it's fanbase? Because as soon as I booted up a Black Ops server I encountered a hacker, was called all manner of racial slurs, homosexual slurs, gloating, and witnessed myself dying 30 times in just over a minute.
TL;DR: I don't hate the games, just the abusive fanbase. Call of Duty only gets hate because of them.