My opinion:
There are haters everywhere, I agree. In the case of headphone reviews, there are both haters, and hypers. We're free to read and find reviewers who generally have the same tastes as ourselves, or who give reviews which we can generally agree with. In the case of the 700's, the reviewers who I've found to be in alignment with are mostly unanimous in their verdict. But headphones can also be seen as a technical tool... they are transducers after all, converting electrical signals into sound.
For the sake of what I know to sound true, I find frequency response graphs, and cumulative spectral decay plots to be effective in identifying sound signature "deal breakers"...
HD-650 - lacking sub bass. Has a fairly linear response across most of the mid frequency range. Treble region is perhaps missing some detail information in the 4-5kHz range, but generally fairly smooth and rolled off. Nothing looks to be offensive, and no real spikes to speak of. I personally find the sound signature to match what I see in the graphs on these headphones... what the graph/plots don't show is their ability to scale with gear. Plugged into craptastic gear, they will sound boring... as you upgrade to better gear, these headphones will improve at every step. They are truly superb at scaling with gear. This may seem like something to be taken for granted, but some headphones will sound as good as they ever will regardless of gear. As for flaws of the 650's, perhaps it would be people who don't take the time to try them with better amps, or people who find them overly warm/lacking treble energy. Not a problem for myself... these are keepers in every way.
HD-800 - again, a fairly smooth looking response throughout. There is noticeable upper midrange scooping, or perhaps an emphasis on the treble, which in my opinion is tamed with the Anax mods. Much more energy in the treble region in comparison with the 650's, which translates into their revealing nature. These headphones are much more picky than the 650's, in that they are superb at revealing both excellent recordings, or flaws in your source material. I believe the reason why the 800's are so popular is because they stay true to the Sennheiser sound, which to me is the clarity I mentioned in my other post. The upper midrange scooping and/or emphasis on treble could be heard as the headphones lacking warmth. I do believe this is dependent on the source, but I am also a fan of the mod, as I find it removes some of that treble energy, and allows for the mids to come through. I don't find them to be scooped out sounding, but I do find them to be extremely revealing. For good recordings, these headphones are amazing. I would also suggest that both DAC and amp need to be thoughtfully chosen for driving these. They will pick up on any inherent flaws and expose them.
HD-700 - Ok, awesome... has some of the sub bass the 650 was lacking, but still generally lacks in comparison with the 800's. Mids are looking fairly even and nicely responsive... oh, wait, here is 1kHz and I'm beginning to scoop. Scoop scoop scoop. Ahhh, ok, no worries... this is just a bit more scooped than the 800's... no wait, it's much more scooped. We have lost a lot of upper midrange detail here. And treble. Pull up... pull up... pull up... JESUS!!! What did you do??? You could have just rolled off nicely like the 650's, but instead, you spiked and created this crazy intense ringing that will surely be a deal breaker for people who want an even keeled treble response. This needs to be fixed.
Let's assume the treble spike does become fixed... we are still left with a "huge" lack of information in that upper midrange region... I think this is truly a nail-in-the-coffin deal breaker. I just can't see this ending well... but I am entirely open to whatever can be done. I'm also not a fan of EQ, but maybe it will require some of that as well...