Yeah, that was really cool of the 2D Boys to put a demo up, and it's a pretty hefty demo at that. I've played through almost all of it, and it is a really great, little game. But honestly, I think it's a tad over-rated. It seems to be the consensus among game reviewers that old-school equals "good" (see uber-over-rated Mega Man 9 for more on that). It's definitely worthy of the $15 price tag, in my opinion, and I plan on buying the full Wii version at some point, but a "9.5"? (IGN's score of the game.) Meh...I don't think so.
Of course, considering that it was two guys (three at certain stages) who created it, sure, it's easy to be a gusher over it. Nonetheless, I don't give extra credit for those things. I personally base my opinion on how good a game is versus the price tag. Period. 2D Boy gets a huge golf clap on top of everything else, but that's about it. Still, a great game, though. Maybe if I play the full version I'll change my opinion and bleed roses too.