Advantages: all-new 32bit code, based on the Nuendo audio engine. Optimized for W2K/XP, so it does run more efficiently than VST32/W98SE did (in my limited current experience). Does a number of things better, because the code was designed for it from the outset instead of being bandaided to do things as an afterthought. Foremost: the inspector replaces 75% of all the existing windows. The track mixer grows to allow you to pop up efx or sends, without having to pop yet another window to get the sends for a single channel. Lots more buses, better bus handling, yadda yadda. But:
Cons: it's not Cubase, it's much more Nuendo-plus-MIDI. It's a different paradigm: you either love it or hate it, seems like. I like it a lot, just FYI. It does an absolutely shit job of importing existing Cubase tunes: you really need to start from scratch with new material with it, unless you didn't edit much or use any of the automation features...
It's a tough call. Go to the forums on cubase.net to look at the outright warfare between the love-it and hate-it crowds. I personally think it is a valid tool, and it is a step ahead, but others _vehemently_ disagree. I also think that the audio engine is significantly (audibly!) better than the one in VST32, so for me it is worth the migration. Your mileage, of course, may vary.
Hope that helps. The reaction to this new version is very mixed, just as the reaction to a new screwdriver or wrench with a differently-shaped handle would be. It's a tool. Yes, it works. It's not clear if it'll fit _your_ hand, though.