Overrated: Meze 99 Classics, mostly due to their incredible review from Tyll using the old pads. They sound nothing like that now but somehow still carry the reputation.
Underrated: Shure SRH440. When I tried them in the store I had never heard of them before but immediately thought "WOW these sound good", and sure enough they almost match the Harman Target. I didn't bring them home with me since the comfort was a little meh, but I don't hear much about these and they need to be more talked-about (although I can understand they're not everyone's cup of tea with the high-treble peak).
Exactly where they should be: The M50x. This headphone straddles the line between love and hate for a lot of people without anyone being perfectly reasonable about them, but the love/hate is so equalized that it results in them occupying the market segment they actually should.
They are just a very good reliable headphone that ticks all the boxes, with relatively minor deviations from the Harman Target that make them more "exciting" and a little better for picking out details in monitoring applications (to my knowledge). I've been all over the headphones in this price bracket and nothing else does as good a job with build quality, listener-to-listener consistency, FR balance, flexibility and comfort anywhere near the price.
If the AKG K371 fit you and seal properly they beat the M50x in SQ, but they have serious user-to-user consistency issues.