I don't own any sort of iThingy, so I haven't had a chance to try it myself, but according to reports from other fans, it's a straight port of the original game with slightly enhanced graphics and touchscreen controls. From what I've seen, it looks great, though apparently the controls are a bit wonky. I'm told the iPad version is a bit easier to handle, what with the larger screen and all, but the iPhone and iPod Touch controls can be frustrating. I suppose if you're willing to shell out the money, a controller like the Logitech PowerShellwould help.
Unlike other TR1 downloads (I'm talking to you Steam and GOG!) this one includes the four Unfinished Business bonus levels. Just tap the icon with the little gray squares to switch between the main game and the add-on.
In this short video, James from AppSpy takes the game for a spin on the iPhone 5 and gets mauled by bats while sorting the controls. ;) Looks like fun!
At £0.99/€0.89/$0.99 you really can't go wrong. Visit the App Store for details. If you have a chance to play it, please leave a comment letting me know what you think.