Just played about an hour of this game, and I'm really glad that I decided to pick it up. Had some dollars sitting on the eShop and figured it was better to go ahead and just purchase something instead of sitting on my hands waiting for Smash to come out.
The feel of this game is amazing. It definitely exudes the same charm and difficulty of the Zero line of games, though it's slightly easier.
The challenges, of course, are the main highlight of the title for me, and it's great to see them in there. The whole point of the Zero games has arguably always been to replay them, to see how good you could get at each of the stages and how high you could rank. I've probably gone through the first stage at least 3 times by now, and have managed to go from B- to A-rank (though S-rank still eludes me; haven't figured out all the mechanics towards racking up score yet).
I was initially put off by the main combat mechanic - tag, then shock - but having now gone through at least 2 of the bosses, I can say it works very well. It's not the same as Zero, and it's for the best. Having to tag, stop, charge, gives you a nice pattern to settle into, especially if you're going through a stage for a second go. You start to use down-time and kill-time as thinking moments - "Where to go next? What's the next room set up like? Do I have to dash, jump, charge, heal? How many skill points do I have left? Should I save them?"
It's all great fun. If anybody is reading this thread and waiting for a reason to pick it up, outside of hoping for a sale or price drop, it really is a nice little title. I read the IGN review previously and, while the review editor kept harping on and on about the minimal enemy variety, you really don't care once you're in the game. It's less about the foes and more about you - how well you can dash, how motivated you are to get through a stage faster and faster.
Will post again when I've had a chance to completely finish the game and can look back at it in it's entirety. Right now, though? Such a blast to play.