If you've ever played thru the Madden franchise with multiple people (not online) or just by yourself, it looks to be very similar to that. Each user controls a team, play their games, manages the roster, trades, all that good stuff. The commisioner of the league will be able to set how many games the season is, quarter length, date/times to play, difficulty level, all the things you control and more than in previous games from what I've read/seen.
Really cool - You'll also be able to manage and control your team from your computer rather than just on the PS3. For example, if you want to adjust your depth chart, propose/view trades, gameplan, pretty much all the stuff other than actually playing the games, you'll be able to do from any computer, similar to controling your fantasy football team.
So if you're worried you won't have time to keep up with the league, don't fret b/c with this new feature you can manage your team while you're on your computer at work or sitting at home. I believe you can even set it up so you recieve txt message or email updates anytime someone proposes a trade to you so you can review it or decline it.