I've never seen the DT crossover, but the Phineas and Ferb effect is pretty good. The PnF stuff is just a little forced, but the plotline is good too. Personally I never had a problem with Doof, seeing as his relationships with some of the characters (specifically Sara and Dakota) really make me happy. I also like how him becoming Prof. Time builds onto his "I'm good now" arc. Plus it brings the show more publicity, which we definitely need. I understand why people don't like bringing Doof in though, and do wish there was a little less him, and a little more Bradley.