Just to take a few examples of the things i found unbalanced/needless or just didn't like:
Wood Elf Army.
Wardancers ignore armour on 6's and have an attack of 5
Waywatchers are cheaper and better than regular elven archers and ignore armour on 6's
Young Dwarf.
A personal bugbear i think but i really think flame cannon are OPand allowing 3 per 1000 poins is madness

Losing access to 3 of 4 troll slayer units in a typical (for us) game in return for access to dirt cheap militia and some ninja tanks... i mean miners is a no brainer. Giving those remaining slayers some free movement is of very dubious merit IMO.
Also... why exactly do they need the addition of a terror causing maniac for so few points?
I already consider the dwarves to be one of the most powerful army's and just don't see justification for these buffs?
Nippon/Cathay.
One of our regulars really wants to play one of these which is reason enough to raise suspicion

Slayer Dwarf.
We trialed these and they were bonkers... not so much OP as WTF?
Dwarf Engineer.
Do i really need to explain what is wrong with an army that can have 6 flame cannons and 4 normal cannons?
Do I really need to explain why allowing the player to spend 130 points to give all that artillery a +1 to hit is a really bad idea?
Really, i have nothing good to say about this army... I have never played a less enjoyable game than playing against this (3 times!!!) Everything else in the book gets tainted for being close to it

The rest.
There isn't anything terrible about the others (that i can see) it's just debatable how much they add to the game. Grimgor's seems a typical example of adding flavour that adds nothing much to the game. A new and awkward mechanic that just seems to be a heavy handed solution to orcs low command. I don't really think this needs solving in the 1st place? Others just seem a bit too niche so we put a motitorium on using them and rather than just pick and choose it was felt (mostly by me) that it was easier to just limit army selection to the main lists and the tournament options. I am sure we will re-appraise that at some point but not for a while.
Oh, and just to answer Frogbear... Nothing particularly wrong with the Chaos Dwarf at a glance. I am pretty sure we did play that one once or twice and i can't remember having any substantial issue with it. Not keen on giving it access to so much cheap orc and hobgoblin cannon fodder but thats more a niggle than a complaint.