I've driven the new M5 extensively (and the M6 but only for a short amount of time) and it's great if you're looking for a fast commuter car. It's really comfortable, spacious, and fast. It's REALLY FAST for a sedan that size plus the torque hits early at about 1500-2000 rpm. Downside is that it's so big that you don't feel the speed or the road for that matter. When I was driving it, I would frequently be going at 60-70 mph but thought I was going 40. I can't compare it to the E60 M5 because the last time I drove one was 5 years ago.
Comparing it to my M, I think that the M3 is more fun to drive because you feel more connected with the car. I think it's from the hydraulic steering along with all the noise associated with the car such as high revving, road noise, etc. With the M5 the steering is very light and artificial. The engine noise is there because of the stereo but nothing else. You feel like you're in a room with a audio recording playing in the background which I personally found kind of weird.
I personally think(hope) the new M3 will be fun to drive because it's the bread and butter of ///M. I'm pretty sure BMW will find ways to make it fun and enjoyable to drive.