Most likely I'm too specific about it, but I see quite some shows mentioned that I'd not really consider underrated or unrecognised. Firefly is one of my all time favourites but not really underrated or unrecognised. Or Fringe, possibly not even From (of which I'll just say I very much hope they have an ending planned because I don't want it to end lost like Lost).
Perfect examples of underrated or unrecognised shows are Galavant and Utopia, mentioned by others, they are brilliant.
In a similar direction I'd say Dead Set, a UK show that really surprised me ages ago but never see mentioned. https://imdb.com/title/tt1285482/
Maybe I should include also Dr Horrible's Sing Along Blog, but that may be a lot less underrated and it's a minishow only.