Playing competatively (ie, against real opponents) is not fun for anybody who likes to play a football game like how it is played in real life. There is very little risk online for playing uncharacteristic of an NFL team... in real life, if a coach calls 4 consecutive hail marys, and they all land incomplete or get intercepted, the coach is fired. In Madden, not only is there no risk, but the reward often outweighs the risk.. one of those will be caught and one of those will turn into a touch down (maybe this doesn't happen anymore, but it still applies to the other over-used plays like screens in M'10). It's the same with unconventional playcalling in the 4th quarter, and simply taking the ability away from gamers doesn't make sense, but the lack of penalty or punishment for unconventional all reward no risk play takes away from the online component of football games.
Additionally, games simply take too long online. I don't like being in a 1 on 1 chat room with somebody for 50 minutes... having to make passive small talk if we're both on the mic... It is intensely awkward.
NCAA used to allow you to play the OT Drill mode online, and the mode was tons of fun. It'd take anywhere from 5 - 15 minutes and you'd get in a quick game. If Madden could implement an online mode that didn't take such a time committment, I'd like it.
Additionally, there are few ways to have semi-competative fun with friends. The Madden Ultimate Team mode was something that had the ability to be a blast playing with friends, but the Madden crew totally didn't think the whole mode through and you couldn't play against your friends with the mode... it was ridiculous, the one mode that would be the most fun to play with your friends, building a team and having a unique experience... barred you from playing with friends. I wrote about
this topic here and how the mode could easily be improved and include that.