Christmas in January is probably one of my favorite movies ever, but it only has a 5.57 on MAL. It's only 46 minutes and it's the most densely good anime I've ever seen. As in like, it's the best anime ever per-minute.

If you have a MAL account, you can plug in your username to anime.plus and you can view a bunch of stats including what your biggest score differences are. Here's everything that I have rated around +2 points higher than the average score:

Suzumiya Haruhi no Yuuutsu (2009)	10	7.24	+2.76
Paniponi Dash!	10	7.44	+2.56
1-gatsu ni wa Christmas	8	5.57	+2.43
Kareshi Kanojo no Jijou	10	7.60	+2.40
Gamers!	9	6.72	+2.28
B-gata H-kei	9	6.82	+2.18
Suzumiya Haruhi no Yuuutsu	10	7.82	+2.18
Hibike! Euphonium	10	8.03	+1.97

All of these I would say are quite underrated, though Kare Kano and Hibike! Euphonium are pretty well-renowned. Haruhi is also very popular.