Online Games need to shed their story-driven predecesors
In the age of online gaming, devs need to come to the point where they stop pretending that online combat is a part of a game's lore. With the exception of licensed games (Star Wars) or single-player focused games (Assassin's Creed: Brotherhood), trying to get the online to mesh with pre-made backstory is hindering to the final product.
Too many developers feel pressure to include both single and online play into games. When online was starting out, this was understandable. However, with the online scene booming as it is now, games which wish to focus on multiplayer need to shed half-baked campaign missions that people will only play through for achievements or to get a handle on the game. This can be risky considering if game's online community dies then the game essentially becomes unplayable, but can be remedied with options such as bots, offline multiplayer, and the popular "horde mode" complete with leaderboards which often doubles as a co-op option.
Further more, online game "atmospheres" need to stop sticking to cookie-cutter concepts that ultimately hinder the game itself. Halo is a good example. If the developers didn't need to worry about maintaining the idea that you are a Spartan in a war (rather than a player in a competition as you actually are), they could cater better to the online crowd. Other games also apply a modern, historic, or futuristic atmosphere and then must try to maintain a sense of plausibility when creating abilities and weapons. Forget it; if a feature will make the game better, add it.
Don't get me wrong, there are tons of great online games from many genres. However, I would very much like to see a dev release a game with an online focus based on the theme of: "You are gamers competing in a virtual arena." Focus completely on providing a fair, balanced, fun, challenging online experience with as many effective features and interface options as possible. Get rid of "storylines" and inflexible lore; let the gamers create their own history.
That's my rant.