Even if the minigames were the entire game, is that really a bad thing? I mean, the first game was basically a mini-game collection with some boring filler stuffed in between. The open world of Santa Destroy was far from the draw of that game (and while I haven't played NMH2, didn't they already remove most of that stuff anyways). The draw has pretty much always been the style and the bosses, both of which look to be maintained in this release.
I'd be interested in playing what we've seen so far, and I'm even more interested to see what else is to come.