I like the look of both of Burton's Batmans, but particularly enjoy the darkness of the second one, so no, it is not too dark for me. If he was actually dissed by the studio, then they were mistaken. Burton brought us a comic book Gotham for sure. I would have watched another Burton installment, but as it was, I did not see any subsequent Batman release.
Michelle Pfeiffer was very good, as was Danny DeVito, as was Christopher Walken, as was Michael Keaton. I enjoyed what each of them brought to their respective roles. As much as I liked Jack Nicholson's powerful persona in his portrayal of The Joker in the first film, it was more enjoyable that Batman had several adversaries in the second one.
To answer your question about Pfeiffer: she was excellent at portraying the playful, vengeful, cold, sexy, crazy kitty that she was. I can't really think of another actress of that time that would have done it better.