Following the initial novelty of making music on a phone, we're now slightly jaded. We want 'serious' features like effects, quantisation, timestretching, automation, mixing, MIDI and straight-up good sounds.
BeatMaker 2 offers all of these, providing a sequencer, two types of instrument (a drum machine and a sample-based synth with a large and varied preset bank) and a mixer. Sounds can be recorded in from the mic or pulled from your iTunes library; swing can be added; the mixer looks great; tracks/MIDI can be uploaded direct to SoundCloud or exported; and you can swap audio pasteboard clips to and from iOS. And that's just for starters.
BeatMaker 2 is going squarely up against the superb NanoStudio, but it's hard to say if one eclipses the other. For example, NanoStudio offers up a true synthesiser with sample playback to boot, while BeatMaker has only a (well spec'd) sampler. But then BeatMaker doesn't restrict the number of instrument tracks available - it's limited only by your hardware.
BeatMaker also trumps NanoStudio's two fixed (but fairly flexible) effects per instrument, with your choice of any three out of a roster of ten. But the interfaces are generic slider-based affairs, which doesn't inspire creativity or excitement, whereas NanoStudio's have a characterful 'custom built' aesthetic and entice you to twiddle their knobs.
BeatMaker 2 isn't perfect. It doesn't replace your proper studio and we did experience a few quite irritating hang-ups and glitches (which we hope are ironed out soon). However, you can certainly have plenty of fun with it and create some very pro-sounding results.