I agree with chelstondave. It really is about what you enjoy. If you liked the HD650s then you won't get anything like the Sennheiser sound from another brand. I still love my HD595s which I have had for 10 years. However I also wouldn't be without my Beyer DT770PROs, which not only provide me with a closed back option (perfect when my wife is watching TV in the same room) but a different sound that suits different moods.
Loads of choice out there on the headphone market. My only advice is to stick to the proper hi-fi brands and, even more than that, I still fell that the experienced headphone names make the best headphones - Sennhesier, Beyer Dynamic, Audio Technica, Grado, Sony, AKG. Of the others I feel NAD's offerings would be worth exploring as would those by B&W, Focal and Musical Fidelity.
Ultiamtely, you have to audition and that should be a lot easier than it used to be given the popularity of headphones.