This game isn't Mario. It doesn't have that guaranteed sales cushion. And that opinion, while I'll tend to agree with it, is in the minority because Super Mario Galaxy sold very well regardless. This is a new ip by a developer with a not so good track record and the game has had a bad reception so far.
"Two generations old" is a lot different then two years old. I'm indifferent to graphical quality, but if it really is like PS2/GCN in graphics, then that speaks enough about its quality.