Wisely, Apple didn’t seek to recreate the Mac version of GarageBand when they ported it to iOS: this is very much a re-imagined piece of software that’s specifically tailored to mobile devices.
Evidence of this comes with the excellent Touch and Smart Instruments, which make creating respectable-sounding keyboard, drum and guitar parts easy and enjoyable. The sequencer works well, too, though the lack of MIDI editing remains a problem (something for version 2 perhaps?).
Crucially, projects started in GarageBand for iOS can be opened in GarageBand for Mac and Logic 9 too, so even if you don’t use it to finish tracks, you know that good ideas can easily have a life beyond your iDevice.