Totally agree. House of 1000 Corpses is tremendous fun, with a great monster and some genuinely scary moments. Devil's Rejects has some scary moments too, but not in the same way. It's a nasty, vile experience, which I'm sure fans delight in but for me it had too many steps too far.
It's not what you do it's the way you do it, and for me DR was just too ugly and perverted. There's a layer of contempt and depravity on top from the director that I found uncomfortable. I guess if that was the directors aim, then job done.