After some initial trepidation about the implementation (namely, bad taste left by MercurySteam, the counter-attack thing, 2.5d usually being awkward), I have to admit, I am really enjoying the game.
I hope it does well, but, if my 7-year old son is any indication, it may be a bit too challenging for some people. Notably, he beat super metroid a few months back (had a lot of help though) and this seems to be a bit harder for him. Part of the problem is the general aggressiveness of common enemies, as everything charges, all the time, to enable the counter mechanic. On the other hand, one of the compromises I particularly like is the metroid "gates." While I sort of hate the artificial gating of areas, it doesn't bother me too much, as I just go about my business in a given area. However, for my son, who appreciates an occasional hint, it gives him somewhere to get a guide post. I really think it is a step up from the more forced guidance of some other metroid titles.
I still think that 2.5d doesn't do the game any real favors, but the implementation isn't bad. I think some of the environments are a bit ugly and the common enemies sort of derpy.
Honestly, I'll be reasonably satisfied if MercurySteam gets another at-bat for the franchise and they put this much care into it.