I'll try the online soon, it's a Saturday night just after launch, so probably crowded, which will make a good test.
Did I mention how beautiful this game is?
I can't understand how people didn't think this game looked too much better than the previous, but perhaps I look at things with a different eye - the amount of geometry alone, I wouldn't be surprised if it had doubled or in places even quadrupled or more. The lighting is even more impressive than before, and there are some shrubs with very long upstanding leaves that have some impressive interaction/animation. Physics have very clearly improved as well - I particularly like how you can dent a minivan from behind for instance mid race just by bumping it with a sturdy enough car.
And the variation is a godsend. Also really like that you can try races from the four different elements and progress more in some, less in others. Also interesting that there are some mission style things in there, like finish the race while crashing max 3 times, or finish it within a certain timelimit, etc.
EDIT: did 11 ranked online matches and a whole slew of offline. The only thing that seemed weak was the voice chat - when it was enabled and people were chatting it wasn't all that good quality. But that may have varying reasons. Another weak spot is the general issue that when you invite friends to your player's list to set up a kind of party/lobby, you can't see what they are currently playing. You can see this through XMB though which makes it a bit silly, but this means you'll look for other MS2 players using XMB first, and then invite them through the game.
Other than that though the experience was flawless and a lot of fun, with deliberate and successful attempts to take each other out etc. I only experienced lag a bit once when the first person had finished already out of 11 races, and I experienced a similar bit of lag once offline exactly once (out of 30+ races I think), so I'm not even sure what the cause is. Stats work too.
The game doesn't install by the way, but does seem to cache stuff to the HDD when loading the levels. Load times are pretty good, only for loading the track really and it takes maybe 20 seconds tops.
The garage view of your car in 3D (optional) has a few fun 'extra's', like revving the engine and 'testing' your car's suspension by leaning it about using the sixaxis.
Motion control play is perfect for me, I've been winning events easily and online I'm not left behind either.