Have been spending some quality time with the E75, but it is still early to give a full impressions. The sound quality is a considerable improvement over the E51 and even the 5310 XpressMusic, though the music player still lacks the usability and features of dedicated DAP like my Walkman.
The QWERTY thumboard is made up of flat keys and feels similar to my old HTC Universal phone. Give a choice, I actually prefer the thumboard from the E71 (which in my honest opinion, is the perfect example of how to do a QWERTY phone), but this isn't too bad. Despite the size, the E75 is pretty hefty (in a good way) and solidly built. It is just slightly thicker than the E51 and has a similar overall footprint. Impressive considering that the E75 has GPS, a better camera and a sliding keyboard...
Some close up pictures to keep you occupied while I get myself more accustomed with the E75:
The E75 is available unlocked for around £300 at Amazon UK and US$450 at Amazon.com