I enjoyed this game a helluva lot, although admittedly, I did only play it for about 5 hours tops.
A lot of the levels are exactly the same as the ones in the first game, such as the levels on the ground, where you only have to take out a certain amount of enemies, etc.
The new addition of space battles was pretty awesome though, they have got to be one of the most fun parts of the game, although I felt quite stupid when I was originally trying to destroy the enemy ships by just shooting at them :"> .
Overall, I'd say its definately worth a buy, if not a rent, but bear in mind I only played it on PS2, and didn't try out internet play, so it may be different on other consoles/PC and may be crap on teh internets .