For 800 MS Points ($10), you are going to get yourself a decent old-school shooter with a new coat of paint shooter. If you are a fan of the series, or a youngun looking for a history lesson, at least check out the demo version.
It's not quite as polished as Namco's XBLA updates (Pac-Man Championship and Galaga Legions), but for the retro fans out there, Infinity Gene still provides plenty of entertainment bang for your buck. Go in knowing what to expect, and you won't be disappointed.
Of all of the remixed Space Invaders games I've played over the past couple of years, Infinity Gene is probably my least favorite. Turning the game into a shmup was a pretty good idea, but the end result is a game that's a bit below average for the genre.