No installation problems, no compatibility issues with Cubase Studio 4. More complex and comprehensive than version 2, with many interesting possibilities (percussions, special agent) but...
... it all goes down the toilet because of the lousy sound quality!!!!
You can hear some sort of hiss at the tail of toms, kick drum and percussion sounds! I first thought it was a sample rate problem (I work at 48 Khz) so I switched to 44.1 Khz with exactly the same result! I didn't have this problem with Groove Agent 2 (which I cannot use with Cubase Studio 4 because of VSTi incompatibility).
Furthermore, you can add percussions to the main drum set but they don't seem to generate MIDI data so they can't be exported to a Midi file if you want to play them with another software (ludicrous!!).
The program isn't stable, some fills seem to "distract" the "drummer" who suddenly decides not to play anymore!!! My computer setup works fine, generally speaking, so I don't think that could be the source of the problems.
I've owned it for 1 week and it's really disappointing, it's much worse than version 2. The features and possibilities are very appealing but the sound quality is definitely not worth the money!
The only positive thing about the samples is the possibility to create Midi files from the provided presets. Out of my despair I bought EZDrummer which is much better in virtually every feature, except maybe for the lack of a "jazz" style. I used Groove Agent 3 to create the drums part of a song and I exported the Midi file in order to play it with EZDrummer. This way I can have decent sounding "human" drums. This is the only reason I give it a 5...
It's too expensive considering the sound quality.
Don't ever buy it!