I realize these are all 'summer is here, sports suck now' boredom threads, but let's define 'overrated' and 'underrated'.
To, me one who is overrated, is one who is unfairly praised by the media or fans, particularly as it relates to their contemporaries throughout the league. This can be on field production, effort, etc. The flipside for underrated. I always look at 'underrated' as the guy people SHOULD be talking about, but are talking about someone else.
For that, I say the most underrated Bear is Martellus Bennett. His stupid mouth and stupid brain overshadow his accomplishments, but when compared to his contemporaries around the league, he's very underrated. He just doesn't come up in conversation when discussing the best TEs in the game. Sure, we know Gronk/Graham/Thomas/etc - if you look at the numbers for last year, he lead the league in receptions (90) in a shit offense that just wasn't on the field much. He's also at the top of all the categories that matter (YPG, YPC, TDs). So to me, that's underrated.
But when I think about underrated, I think Jordy Nelson. Never gets mentioned among the top echelon of WR. All the guy does is make plays. For hockey, the comparison is Nik Hjalmarsson.