I've always wanted to watch Desert Punk and Rainbow sounds interesting, even if there's no Zippy in this one.
I've never really been "pleasantly surprised" by a new anime though. I tend to do my share of research when choosing something to watch, so I don't just pick up random series like I do with videogames and books, where I've found a TON of pleasant surprises.
I made a list of a few shows I like that are under the radar and hidden gems. Off the top, Erin and Kaiba immediately come to mind.
My friend tells me that I would enjoy Desert Punk but I've never seen it. I know it's on Netflix but 20+ episode shows always seem so daunting to start. For manga, I'm not too familiar with it but I really enjoyed Bokurano, Hatsukoi Limited, and Eternal Sabbath. 2/3 of them are in English though so I'm not sure how hidden they actually are.
I have no idea what would be a hidden gem since I don't talk to to many people (who watch anime... this should have been there in the original post :p) but I don't personally know anyone who has watched Minami-ke. I found that series very relaxing and fun. It's a slice of life type show with no plot that focuses around the three Minami sisters.