I don't think it flopped, or at least it will flop on the long run. I mean look at the sales Bayo1 had for each consoles or all DMCs after PS2 era. The highest selling is 1.5M on 80M userbase and was released in 2008 (6 years on the market). I say let's wait some more time until we got some real figures for the sales and judge then.
And also, as said before, comercial and critical success are two different things, usually related, but two different things nonetheless.
As for it being niche, well it depends on what people consider being nice. Outside of the usual heavy hitters, Marios, CoDs, ACs, FIFAs, Uncharteds, Halos, etc, everything else seems to be niche according to some people definition. I wouldn't cal for sure a +1M seller niche for sure, so I wouldn't also call it to some games that sell less than that...







