N.O.V.A. 3 - Not recommended for an iPhone 3GS. The graphics look like crap. Still really fun, though.
Grand Theft Auto 3 iOS - Slow as hell on 3GS. Again, still fun though.
Sonic 4: Episode 2 - HELL YES. Can't recommend this enough.
Well, I like to spend time getting to know a game first before I play multiplayer on it. And the internet on my PS3 is pretty crappy, it's a wonder how I even got the game installed in the first place.
I'd really like to though, but right now the chance is slim. If anything changes though, I'll tell you.
If you get the iPhone version though and it has multiplayer...
I think Blizzard knew about the online issues even before they had released D3, with the test run and all that jazz. They didn't expect how large of an overload they would be getting, considering that you can also download the game instead of buying it through retail.
Nothing that a few additional servers can't fix.