I do make my own music, as it happens, though it is modest. However, this has no bearing on whether I can criticise another person's music. Also, if music is of a genre I do not like, I do not call it crap. Being a follower of OCRemixes for a long time, I feel that while their releases have gradually increased in quality, their projects are very hit and miss. I thoroughly enjoy the Super Metroid project (which is vaguely true to the source material) and the Doom project (widely panned as being nothing like Doom), I find myself unable to enjoy this one.
Remix it and make it different, yes. That's what a remix is. However... if you change the instrumentation, the time signature, the tune, the rhythm and the emotion... it isn't a remix. It's just another song.