Picked it up yesterday, seems really fun. I played a single playthrough through every 150CC GP and won all but two.
I did not play MK Wii, but MK 8 seems far more hectic. Don't know if it's because of 12 players, but all the time it felt like majority of the NPCs stick together and there is a lot of rotation between spots all the time. Makes for some very exciting races. Levels are great, I think Flower Cup was my fav, while Special Cup was incredibly frustrating. I won 6 GPs, lost Leaf Cup on the final turn (what a terrible choke that was, ugh) and barely placed 4th on Special Cup. Well, there sure is some room for improvement!
Cool how Spiny Shell is so rare now, fitting. I barely saw few between all 32 races. Piranha Plant seems somewhat useless though.
Btw, is it worth it learning to drive a bike? I usually play light characters with high mobility and acceleration, but this is so different. I always cut corners but my few attempts at bikes were failed. Are bikes generally superior?