It's possible to point that out without being a total jerk.
The problem is that it uses stolen assets from another game.
That is 100% not ok, even for a tech demo.
(...there are plenty of free game assets out there, creative commons license; drawing attention to yourself by stealing someone elses art is douche behaviour)
I'm not going to stand up and tell someone its mean and unethical put some harsh criticism out about a project which is in itself unethically stealing art assets and associating itself with a brand it has nothing to do with.
If you're happy to accept this project and what it's doing, you should equally be happy to accept it's going to get some flack for it. You can't have it both ways (doing this is ok even tho its unethical AND but its unethical to criticise it and that's bad).
OT: Gamers tend not to have a lot in between hatred and love to begin with, and if you're at all familiar with the current Diablo community, well, Diablo 3 hasn't brought out the most civil side of the fans.