So I attended a local tournament this weekend and though't i'd bring my tzeentch with my grand total of 1 practice games with the army, as predominatly a Stormcast player I have a few conclusions.
1) Tzeentch stuff dies FAST, which I'm not overly fused with as i knew they are a fragile army but my god that 5+ save is rough.
2) Relying on spells for most of your damage output can be dicey, even with pluses to cast if you wiff some rolls if can leave you in a bad position.
3) Never EVER take Tzeentch's fire storm, I successfully cast this every game and i think i rolled a single 6 for the damage.
4) Skyfires are AMAZINGLY stupid in combat, a unit of 9 rolled 20+ attacks.
5) Destiny Dice = best allegiance ability in the game.
Other then that I really enjoyed the Army, I did some pretty tixy stuff with my Tzaangors and destiny dice to get some pretty long bomb charges across the board turn one.
I did loose 2 out of my 3 games *the 2 i lost were down to the wire* but that's all down to poor play on my half, I was mostly using this tournament as a good way to get some decent practice with the army, but as with every practice makes perfect!