Heya,
You'll see very quickly that the Denon D2000 is still, and will always be, an excellent headphone in it's price range. There is a lot of competition there in that range. But not if you consider two things: (1) closed back and (2) sub-bass. The moment you say you want sub-bass, it pretty much takes out most open-headphones, they can do it, but they just can't deliver it the way a closed headphone can. The impact is just so different with a closed headphone when it comes to a big bass slam. So even though there are a lot of headphones in the $200~350 range, you'll find that, well, very few of them compare to the Denon D2000. The D2000 has a better sound stage than most other closed headphones, it has a semi-open internal design with a vent going around the outside shell giving it a great sound stage, plus deep cups. The bass is not overwhelming, it's actually simply linear down to sub-bass regions, so when you hear a bass note, it's as present as something in the mids. Think of it more like an audiophile's headphone that is really bass capable. The mids may be technically slightly recessed, but this applies to every headphone with any slightly emphasis on bass/treble, the moment something has more volume in one frequency than the mids, it's automatically recessed and I think it gets unjustly applied too often. That said, vocals, instruments, etc, all sound great in the D2000 (you'll find they are clear, forward and more natural sounding than the PRO900's sound on vocals and instruments). The treble has a good sparkle to it, they're not dark headphones, they're slightly bright, but they're not over the top bright (PRO900's are very bright, too bright for most).
I went from the PRO900 to the D2000 to the D5000. Final resting headphone for me, closed back wise, is the D5000. The PRO900 was simply too bright, and it was all mid-bass. The mids were drown out, so vocals just sounded weird, not natural, distant. The D2000 and D5000 on the other hand, the bass is more to my preference, big sub-bass presence, way less mid-bass bloat, the mids are great, vocals and instruments sound normal, natural, engaging, and not distant. Treble is bright, has a sparkle, but it's not spiky bright, so it doesn't fatigue me (it does others, but everyone is different and some are sensitive to all headphones with any brightness at all).
Out of all the mid-fi headphones, and I have most of them, the D2000 is still in my opinion and experience one of the best headphones you can get, one of the most complete headphones, because it's signature covers all genres, it's incredibly comfortable, it's incredibly efficient and runs out of anything, and to me does audio more like how speakers would sound than a headphone sounds (sound stage, big sub bass ability). At $200 used, to $300ish or more new (if available), it's just unmatched in the closed headphone category in it's price range to me. There are similar ones, but so far, nothing has really taken it down for me. You can look at my selection to see what it's been put against if you care to.
Very best,
