I’ve been meaning to reply to this for a while now.

I got my mnm back in 2007. It was my first real piece of hardware (I had also acquired a monome earlier that year). It really changed things for me since I was so used to mousing about when making music. While it limited my options, it also offered me a completely new palette to work with which made me much more aware of the sounds I was making. It’s been the staple of my music ever since.

Coming from the A4, you’ll have no problem wrapping your head around working with the mnm. As everyone has said, it’s not easy to get the sounds you want right off the bat, but with persistence, you’ll get what you want. I’d cleaning out all the stock patterns/kits though. That’s what I did when I first got mine and it’s really helped me learn in the ins/outs of the mnm.
I highly recommended figuring out a layout for your kits so that you don’t have to think too much when tweaking. Also, be sure to utilize the following to get new/interesting sounds:

  1. Use your LFOs!
  2. Experiment with the different types of trigs.
  3. Play around with swing to give your instruments a more human feel.
  4. I’d stay away from using the effects/routing options until you’ve a firm grasp on creating kits etc.
  5. MIDI up some hardware and/or some VSTs to learn the midi sequencer.
  6. And finally, RTFM…

In any case, just experiment and have fun!