AotC: I thought it was good. My initial impression of the acting was that is was absolutely awful (far worse than what we saw in TPM) and the dialogue the actors and actresses had to speak with was even worse, and yet I still strangely had the impression that the movie was fairly entertaining (though that battle at the end made no sense and seemed totally disconnected from the rest of the movie and Yoda's fight scene was silly and completely sensationalistic).
RotS: After my first viewing I thought it was perhaps the best film of the series [edit: the prequels] (though I think this was mostly wishful thinking). The acting was still bad (though only at TPM levels and not as bad as what we saw in AotC) and I knew the film was way too long and filled with useless crap, but I still managed to like it somehow. Looking back now I'm pretty sure that I was disoriented by the hyper pacing of the film.
Now I think that Phantom Menace isn't nearly as good as I initially had (particularly, the more boring DVD cut), but I still think it's the only prequel that has actual merit. Pittrek complained earlier that there was no story in TPM, but AotC and RotS have less of a story. At the most you could argue that AotC is a mystery and that RotS is about the origin of Vader, but that's really reaching for something as far as I'm concerned (since the first is barely significant and the second is not a unifying concept for the film in which it is placed). In TPM you had a war to liberate a planet from a corrupt political power; its very simple, self-contained, and fun (the only odd parts of the film's story deal with Anakin in the sense that they feel tacked on, but I consider that an interlude).