Initial impressions were in-line with the other reviews on the forums: dark, overbearing bass. I immediately performed the astroid-mod (removing the black foam center from the pads) and also opened them up and lined the grills with tin-foil based on another mod I found on this forum. Wow! The sound cleaned up immediately with the highs and mids coming through clearer, although they still weren't where they should be, so I left them playing pink noise and sine sweeps overnight for a few days. These don't need an amp, but the bass does tighten up and the mids come out stronger when connecting them to a FiiO e5. These sound surprisingly good for jazz and classical, but feel a little slow for rock/electronica and generally "busy" songs.
 
Comparing them to the PortaPros... I still prefer the PortaPros. The HD238 feel less enveloping and I liked the forward way that the PortaPros presented the highs, but this is purely subjective. I tend to use these (and the PortaPros) on the go and I like to have something that gives a punchy presentation. The Senns are overall smoother, but I have too many mixed feelings about them to call them excellent. If they were priced at the MSRP of $100 I'd definitely say no, but for $32 these are an absolute steal.