Everything and nothing, of course.
First of all, TOA was released too soon with too little testing. Many of the encounters were bugged or just much too difficult. Lots of things have been fixed and I think the furor is dying down.
Some people were disappointed because TOA is all PvE. Some people felt, and may still feel, that the Master Level Abilities are overpowering. Some people felt, and may still feel, that some of the Artifacts are overpowering.
No doubt all opinions are valid, but not overwhelminging true. DAOC is still a good game.