If I decide I want to play poker at 9am in the UK, Party is one of the few places I could go to get a choice of games, such is the size of its userbase. There are thousands of games, at all limits, to choose from. For that alone, it is worth signing up. There are also many tournaments in which you can parlay up from a few dollars to very large sums indeed.
With a lot of players comes a lot of bad players. That's always good to know! Half the battle on-line is to find players who will call off their chips against your nut hand.
I am not a great fan of the software but at least it works. I believe it will be revamped soon anyway. I look forward to that.