TUAW's Daily App: Streets of Rage 2
Yes, the classic beat-em-up joined Sega's iOS library a little while back, and you can get in on the fun for US$2.99. The second iteration in the very famous 2D fighting series features Skate, Axel, Blaze and Max going to war against Mr. X and his army through all eight levels of the original game.
Unfortunately, this version is short on extras. There's no Game Center integration. There is local Bluetooth multiplayer, but that's about it. The controls, as you can see above, aren't much more than serviceable, either. In other words, this is more a straight port than anything else. You can actually play the original version in Japanese, but you have to switch your device's language to Japanese, and even then, the differences aren't that big a deal.
Still, Streets of Rage 2 is a solid beat-em-up title, and you might have fond memories of this one on your Sega Genesis or Sega Game Gear. If the price is too high, just hang on -- Sega routinely puts its titles on sale, and this one is likely to drop in the future.