EG:rRootage is one of Cho's finest (and oldest) games, a vertical one-screen shooter with tons of levels and four distinct game modes, and while modes can often seem like little bonuses in shmups, in rRootage they're the whole focus. The core of the game is boss fights. Every level is one giant ship at the top of the screen and your ship at the bottom, which is in fact just a hitbox with a shell. The boss ship fires a pile of bullets, and will change form several times throughout each stage, which also varies up the shooting patterns. And there's one tiny, crucial other detail: the closer you are, the more damage you do.
TouchArcade: Coincidentally on the heels of talk about how long people are entitled to updates on games comes news of another App Store classic getting a maintenance update. rRootage Online HD [$0.99], the paid and universal version of Kenta Cho's classic freeware shmup, ported to iOS, has just gotten an update to make the game work on iOS 8, and to support iPhone 6 & Plus resolutions.
Portable Gamer: Remember that old adage of never judging a book by its cover? These wise words are never truer than when you take a look at rRootage. What comes across as a game lacking in play style, limited visuals, and gaming depth equal to that of a water drop on your iPhone screen will quickly prove to you just why simple looks are so devilishly deceiving.
Oh yeah! Kenta Cho's stuff is awesome, this comes highly recommended!
Of course, you can just download the PC versions for free.