i'm in the beta and a fan of HOMM. VI is good and worth buying _IF_ you liked V. It is more like V than anything else. Regarding bugs in V: if you buy the "Tribes" stand-alone, you get V without the bugs.
the big changes are:
1. resource strategies have been simplified, which I think was a mistake, but not a dealbreaker.
2. the town screen is a step backward: with lots of icons and a GUI that is too fiddly. Someone should be fired for doing that.
3. The combat is as excellent as ever -- deep and multi-layered. Very pretty game if you have a PC that can run it at High.
4. the wonky camera in V is sorta fixed, but only because you now use a fixed camera angle. It is better than V.