1) Focus of wizards on blasting/controlling, and the removal of most 'utility' magic to rituals
2) The degree to which so many abilities are: Damage X plus move figure Y spaces....(frankly, in my dream 4th edition you get rid of almost all these shift-the-pawns powers)
3) Horribly designed (though admittedly corner case) abilities that have some damaging effect on a MISS...thinking here of (oddly enough) the power Orcus has that can potentially do more damage to you on a MISS than on a hit. (Details: Touch of Death...I have a max hit points of 100 and a Bloodied of 50....I am down to 29 hit points...if he hits me I take 29 to drop to 0, if he misses me I take 50 to drop to negative 21 and about halfway to completely dead)
I will admit that I am not clever enough at this moment to think of any supplemental material that could resolve my biggest issues and still be compatible fully with core 4E, but I think that if anyone could do it you or Mr. Cook could.