Personally, I do miss C4 days. Those were good times. Mid rate off servers had some really great communities.
My biggest problem is the more you add to classes, the harder it is to balance them. Not only that, but there's power creep to consider too. That is, CP, HP, and MP haven't exactly kept up with the new power provided from the latest armors, weapons, and skills.
On high rate servers this is VERY noticable. On low rates it's not as bad, but still noticable in the later levels.
Mostly, people have issues with the lack of balance that the new items and skills bring. Back in C4 days, you KNEW what classes did what and everyone was for the most part, pretty happy with their role (though prophets, bds, and sws will always QQ).