There's nothing in '89 that's as crazy as Batman Returns. Nothing.
Joker didn't start coughing up thick bile from his ****ing liver in his death scene. There wasn't a sexual innuendo every 5 minutes. Penguin and his gang of triangle circus terrorists make the Joker from the first film look normal. Oh, and it never snowed!
Batman 1989 was grounded in some 30s/40s crime reality, Batman Returns? It's a Gothic fairy tale land with Ice princesses and rocket penguins. They couldn't be further apart. The shift in "universe" was just as jarring as the jump from Dark Knight to TDKR.
I think the only risk Burton took in the first film was moving away from the 60s since that show was so engrained pop culture. Taking on a "dark Batman" was the only risk, and it could have backfired. Well, that and the casting of Keaton along with things like the black Batman armor (instead of a grey and black leotard).