If your not playing this game on at least hard mode, your doing it wrong!
This game definitly isn't perfect but if you challenge yourself, your in for a really intense, controller gripping experience.
There are 3 single player campaigns to play through, each lasting around 5 hours or so, I would recommend playing as marine to start with.
The multiplayer is alot of fun if you can get into a game, I wouldn't recommend ranked matches, they aren't worth the headache. Don't expect to jump in and rip it up though, it will take awhile to get good enough to take down the hardcore players.
The Hunter edition is the way to go, as you get the extra maps and the coolest extra ever, a halfsize (maybe bigger) facehugger with bendable legs. Worth it just for the facehugger.