Ok still compiling details/review (sorry, super busy) but to give you the short version:
1. The critical question of AF....it's undoubtedly better but far from perfect. I can guarantee you that any AF annoyance you had with the M will carry on with the M2. You won't stop swearing by upgrading, but you will definitely do less of it. It's worth mentioning that I don't think the AF on the M is as anywhere near as bad as people claim.
2. It supports Wifi, but in such a way that is certainly disappointing. For wireless tethering, I would rate the experience somewhat on par with the Sony A7. It works, but nothing thrilling. It still does not support wired tethering which would help dispel majority of my angsty angst feelings against Canon for crippling these amazing creatures.
3. It's even smaller and lighter. The grip is a smidge different. Definitely improved.
4. Takes the exact same battery. My 3rd party Opteka batteries worked fine in it (as with the EOS M).
5. It uses different firmware. Version I had was 1.0.2 for the M2. This means you cannot currently run Tragic Lantern or Magic Lantern, which imo basically ends the decision making process right there. I find focus peaking in particular to be of critical benefit with EOS M.
6. Noise seems immeasurably better. I tested up to 12800 and frankly it's quite lovely and very usable compared to the original M.
So overall, is it worth your money? As always it's up to you. At the time of this writing you can get at least the EOS M and a lens for $300, whereas the M2 body alone is about $650. I would say:
-if you do NOT have an M, and you absolutely do not care about Tragic Lantern then absolutely
-if you already have an M, then I would say don't bother
-if you don't know which to get, get the M
There is no doubt in my mind that BOTH cameras have an undeserved bad reputation. If you're on a budget (or just cheap like me) I promise you that the M is BAR NONE the best way to get started in photography.
Happy shooting! =)