It's been pretty good for me with new releases. I mean, it's not perfect but I listen to mostly indie rock and it's turned me on to a lot of stuff I enjoy, and it never suggests top 40. I also never use the thumbs up/down.
Perhaps one of the problems is that the music I listen isn't well defined in terms of genre - songs on the same album can vary significantly. However, I guess mostly post hardcore and progressive rock - there are bands/artists in these genres I like, but others I have absolutely no interest in. However, I also have lots of "rock", punk rock and some pop rock stuff in my library. I mostly get a lot of metal and hardcore recommendations which I'm simply not interested in. It's also not unusual for me to see rap and R&B recommendations, which I'm unlikely to be interested in (although some songs I like may be defined as such).
It's been pretty good for me with new releases. I mean, it's not perfect but I listen to mostly indie rock and it's turned me on to a lot of stuff I enjoy, and it never suggests top 40. I also never use the thumbs up/down.