Having previously had HD660 Pro I bought 330s for casual listening - semi-open give me less pressure strain and I enjoy being able to hear my surroundings better when someone wants to talk to me.
Sound is good. At first, I wanted to say they don't sound nearly as good as HD660 Pro, but they are just different. I'd say 660s sound great with rock/metal since they have more kick to them and the bass is obviously better, 330s work well with pop/folk where the voice feels more natural. But overall I feel like it's a matter of ears getting used to them cause the base is pretty good for both. At their price point they sound well.
Surprisingly, despite both 330 and 660 having the same exact construction (side for the mesh/panel, of course), the 330s seem to have sort of weirdly shaped pads, left top and right bottom are bent in, which makes them less comfortable. I feel like they'll set in soon, they're getting better, but still... Then, the right-side height control is squeaky. Not sure if it's a manufacturing issue (original gloss foil was in place and everything seemed to be packed as original) or B-stock sold as A-stock (there was some minor box damage). Neither 32Ω nor 150Ω versions of HD660 Pro I had were affected in this way.
