I don't get surprises too often, mostly because i know that being biased about things like the hype, the fanbase and stuff usually turns out to be something bad and you only finish getting dissapointed. But still i have some series like that.
A good surprise for me was Busou Renkin, it was just a super shounen series with a butterfly guy as a villain for me, but when i started to watch it i got a good surprise, first of all things because it was too easy to watch, the episodes passed really fast and yeah, it was entertaining. Yeah, it's not THAT great, but still i got more than i anticipated.