A few things to add:

• What music do you listen to? The 600-series tend to excel well with anything that emphasizes the mids strongly - especially with regards to vocals and acoustic instruments. Despite how revered they may be, I don't find them to be great for bass heavy music or for eye ball popping dynamics.
• How long have you used the HD599? If they've been your daily drivers for years on end, it's going to take time to adjust to a new pair of headphones, regardless if it's the HD600 or anything else, for that matter.
• Jumping off the above question about length of usage, I would actually suggest listening to them without applying any EQ for a week or two straight, at least. Especially the Harman EQ profiles that tend to emphasize bass shelves that serve to emphasize the blurry bass region these headphones tend to have.
• Often, people feel naturally compelled to have this "love at first sight" sensation, but in my experiences the headphones that immediately wow'ed me are the ones I rarely listen to, whereas the ones that I grew to love over time are mainstay staples of my collection.
• Lastly, keep in mind that these headphones have a legacy that has endured the better part of three decades. Naturally, the rose-colored fondness comes from a period where we didn't have nearly the amount of variety and options that exist today.

At the end of the day, even though the HD600 is popular, there are going to be people out there who don't like it, and that's ok. There's plenty of options out there available for the choosing, so it's just a matter of making sure you've given yourself a fair amount of time, before moving on, because if expectations are not in check, then you're going to have the same problem with all other headphones as well.