I've used both Live and PSN and can't really tell the difference. Free > not free. From my perspective, Sony are offering a service which is easily on par with Live, for free. Win. I actually like the online setup on the PS3 better too, the friends list is so much easier to use without all the bulky avatar crap and huge icons. The PS store is also really easy to access from the same menu.
Oh! And Assassin's Creed 2 I really like as well. However I really need to get on the PS3 more so I can finish some of these games... However I don't see that happening when Starcraft 2 comes out next tuesday. In fact I don't see much else happening at all.
The enjoyment of MW2 is an illusion. You think you're having fun, then there's a knock at the door and someone complaining about the extremely loud profanities emanating from your house.....
Favourite PS3 game would have to be red dead at the moment, also really enjoyed modern warfare 2, and of course you can't go past a good session of Little Big Planet!
Red Dead has certainly been popular, though people seem to have mixed opinions once they play it.