Let me start by saying that, yes, the menu system is awful. A 2-line display is not enough to reveal the power that this machine has.
Now that that's over with -- this is by far the most powerful drum multi-pad available. This is the first multi-pad with features comparable to a full e-kit module. Because Yamaha gives you full control over the MIDI layer, you have capabilities not even conceivable on other multi-pads. You can hook up a trigger-to-midi controller and play additional sounds per kit (i.e., sounds that aren't assigned directly to pads). You can hook up a MIDI keyboard and play an entirely different sound set (on a different MIDI channel -- for example, you can have a drum set assigned to the pads on channel 10, then plug in a keyboard and play a grand piano sound simultaneously on channel 1).
It has more pads, more inputs (including a 3-zone snare input), full MIDI capability, hi-hat functionality, and can playback your own samples. 64MB isn't a lot, but honestly, for drum sounds, that's a LOT of time. If you DO need more sounds, because you have access to the MIDI layer, you can control an external sampler directly from these pads (including program changes / control changes).
To be short -- this is a RIDICULOUSLY powerful machine, orders of magnitude more powerful than any other multi-pad available. If you can look past the rough interface and limited on-board sample space, I _highly_ recommend this!