Battlefield 2 on the PC was amazing. Huge maps, great community and always fun. Bad Company 2 on 360 was a lonely afair. Unless you had friends with you in a party you never heard a peep on the microphone and everyone was out for themselves.
Well I gave Halo Reach a go and it has the huge maps and vehicles that you get with Battlefield, it has the awesome community and the support for this game is immense. Also it's easier to just jump in a match if you want to mess around, but you can really customize the experience if you want for custom matches. Also with Forge and Waypoint you have a massive community around this game.
The other awesome thing is 4-player co-op over Live or locally. It doesn't get much better.