This is part of Capcom's holiday sale for Valentine's Day (which is probably also intended to target some new Verizon customers), but Devil May Cry 4 refrain is a pretty good port of the console action game anyway. It features a character named Nero fighting with both guns and a big sword through all kinds of demonic baddies, with the standard Devil May Cry action combos building up as you play along. Unfortunately, like most of these games, buttons are merely overlays on the touchscreen, so really dedicated action gamers may not enjoy the lack of tactile controls. But if you like this action genre at all, DMC4 refrain is a pretty solid version, albeit obviously scaled down for Apple's platform.
The fact that it's on sale for US$0.99 will probably help seal the deal. Devil May Cry 4 refrain also has Retina Display graphics and full Game Center integration, so it's a full-fledged title to play through. If this doesn't float your boat, don't forget about all of the other sales going on. There are lots of high-end titles out there that you can buy for just a buck right now.