single player on the first one sucks.
multi-player is sooooo much fun!
if you have people to play with, pick this up. if you don't then you might want to pass.
although i heard you they're adding a lot of stuff and some mini games (maybe a traditional shmup).
you can probably find the US release of part 1 for like 5$ (Wartech) and give it a spin ...but like i said, make sure you have some one to play with otherwise it blows.