After going through a fair number of headphones and trying some in shops etc. I think I now have a pretty good idea of what is on the market. Except for the extreme high end flagship models anyway. I initially had some Shure SRH 840 which were just mediocre IMO... Good for professional use maybe but not very fun to listen to and somewhat tinny sounding. I also tried some Grado 325i which were quite entertaining but the treble was far too much and literally obliterated my ear drums, also very uncomfortable on ear design.
Next up was the first pair of headphones I really quite liked... The Denon D2000. Very comfortable and very nice bass on some songs although on other songs it was very monotone boomy type sound which I didn’t like. Midrange was rather recessed and the treble was detailed although too sibilant and fatiguing. This was why I eventually sold them. I would recommend these for electronic trance music and similar as they really are very nice for that sort of music, tbh I would quite like them back just to use for this genre.
My current headphones are Sennheiser HD650 (new version) and honestly I am blown away by these, for classical music and more subtle music types they are incredible and just really really nice to listen to for long periods. The open backed sound and the imaging / soundstage is first class and really is a league above the denons in terms of the actual quality of the sound. I have found myself listening to a lot of classical music and film soundtracks on them because it just sounds so damn nice. Electronic music is definitely not as good as the Denons, there is less bass response and they are not as punchy... Although the soundstage and imaging and overall quality still makes this genre nice to listen to just not as good as the Denons.
So overall for anyone deciding between these two I would say the Sennheisers are a much more refined and overall higher quality sound, stunning for classical music etc. The Denons are more "in your face" and have very good sub bass (on some songs anyway) the treble is OTT imo and the overall quality of the sound and imaging is definitely quite a bit less impressive than the HD650. If you are an electro music listener only then the Denons would be better, but as an overall good all rounder I would highly recommend the sennheisers. I think I have finally found a pair I am happy with, although I might buy some other headphones such as some ultrasones maybe purely for electronic music but the Sennheisers aren't going anywhere! Hope this is useful if anyone is trying to decide.