^^^ I usually can spot retail posters/artwork pretty easily. Now I admit, I prefer when they're tweaked or better yet when it's a complete different design altogether but really that's my own taste and I don't have a problem with retail posters. What makes a great cover imo is the overall layout, how things are 'assembled' together, from graphic elements to text and logos. I always look at them as a whole. If it happens to use retail artwork and it works, fine, and if it's more complex then I'll appreciate the effort even more.

My 0.5 cent ;)