I'm not an audiophile by any stretch but i do enjoy a quality music listening experience. These headphones deliver that for an unbeatable $20. I work in a video production environment; each edit bay is equipped with Sennheiser HD Pro 280 headphones. The Monoprice headphones honestly sound just as good as the 280s. It's really hard to pick between the two, it comes down to personal preference.
I mostly listen to jazz and big band music. With a flat EQ these just sound fantastic to my untrained ear. Maybe a bit bass heavy, not in an obnoxious way though. Mids and treble sound great...maybe a bit rolled off but very smooth sounding. Clarinets and trumpets hold together nicely. A friend listened to some obnoxious rap noise with them and said they were "bangin'". I think that's a compliment. Anyway, I'm quite pleased with the sound.
Compared to the 280's these Monoprice headphones aren't as comfortable. The headband becomes annoying after a while. I'm tempted to purchase an add-on headband for them, it just feels strange buying a $20 accessory for a $20 accessory :-) Isolation is great, though not as good as the 280s. Wear these with music going and you won't hear anyone speaking in a normal voice nearby.
Aside from the headband/pad comfort issue, these are just fantastic. The build seems very durable, probably even more so than the 280s. It's also nice being able to swap the cable out. I've been carrying them around in my bag for a few weeks now with no negative impact. Honestly, they're built well enough I can't imagine ever breaking them.
The point is, these compare well to a nice $100 set of headphones. Really the only reason to choose the 280s over these is the big comfy marshmallow headband that comes on the Sennheisers. If you need something that sounds better than these, you're probably going to spend significantly more money. Order a pair and enjoy!