Space Invaders Infinity Gene really was one of the best games to come out on the iPhone in 2009. It was simple to play, didn't demand a ton of time all at once, and looked and felt beautiful, in a spooky, System Shock 2 sort of way. If you haven't played it yet, download it as soon as you can.
Just today, Taito released an update for the game that adds some really neat things, most notably the ability to play the game as a side scrolling shooter and the ability to purchase unique levels and new ships that are based on other arcade classics like Darius, Metal Black, and Night Striker.
Check out the newly updated promo video that Taito put out. If it doesn't make you want to re-download the game, I don't know what will.