OP, go visit a few forums for phones that have recently been released. The new question isn't "are there any major problems?", but "which major problems should I investigate?" I would challenge any existing SGS2 user to point out a dual-core phone that has fewer issues. You'll find "different" issues, but not "fewer." For now, for me, there's no phone currently out that I'd replace the SGS2 with.
And OP, the direct answer to your question is find the threads on display banding, Wi-FI performance, GPS, 2/3/4G radio, audio, camera, and battery life and if, based on your needs, you're OK with what's been discussed you should be fine.