I would give it a solid 5/10- a decent list but many things you could improve.
Firstly the heralds are illegal- a mistake everyone makes when they first start using HoTs: you can only take 3 upgrades on each, not 4 as you have on these. Then again even if you could have that many upgrades I wouldnt take them: they make the heralds far too expensive. I would cut the icons off both of them as they are very expensive and you dont want the herlads that close anyway (if they are they'll end up in combat... meaning there wouldnt be any point using them as beacons for the flamers, which I assume is the plan).
10 flamers in a list is a little excessive, but not as bad as having them in 2 units. I would split them into 3 units of 3 if you want that many, but personally I use 2 units of 3 at 1500pts and have never really needed more (unless they've mishaped themselves to death- risk of using them agressively). Depending on how you use them I possibly would cut teh bolt off them- if you suicide them in really close to take out nasty enemy units then its not worth it, if you keep them further away from the enemy (which I dont suggest- you'll still die very quickly, possibly before you can get to grips with anything) then bolt is more worthwhile.
Then you find the units of Horrors- havinf that many horrors is great, but in 2 units they'll be toast. Big units have 2 disadvantages- if you get into combat the whole unit is tied into it (and being horrors you'll lose, but probably not very quickly) and when you do shoot something it'll die, but the unit next to it wont (but if you could split fire you can try for both). Small units only really have 1 downside- they give away KPs.
I use horrors in units of 5 with a bolt, until I fill all 6 troop FoCs, then I start making them a little larger. I think Im using something like 6*7 horrors in my 1500pt army currently (havent used it in a while). The huge bonus of that is that if you switched 2 units to 5 then you would have an extra 3 bolts in your army, and would lose little by shooting a vehicle, while do that now and you waste 51 S4 shots...
If you do cut the unit size down scrap the icons- they'll be too vulnerable and will die fast.
If you want an icon unit throw in a unit of 5-7 plaguebearers with the icon... but in this list I would just cut them all and be a little reserved in DS placement, you'll rarely have any problems (and if you lose less then 100pts a game via mishaps then you're better off then taking the 4 icons).
Many people dont like screamers, and if you get more responses almost all of them will tell you to cut them.... but I love the little guys, they are the best tzeentch unit around. I tend to use 3*3 and find uses for them in almost every game. I drop them in early, far away from the enemy then turbo boost up turn 2 as most of my army hits the table, they can then draw combat units away from my army (suicide but can be important), chase tanks, force heavy support tanks to move (robbing them of their shooting, and eventually destroying them), destory the remnants of enemy squads (1-2 last guardsmen arent worth shooting with horros/flamers, but screamers can easily take them out) or just survive till late in the game and jump onto enemy held objectives to block them- some games I've know that I've won by turn 5 since I know the enemy cant get to my objective and I have 3 screamer units able to jump onto his turns 5, 6 and 7 which they cant stop...
The only other suggestion I could make would be to cut a few points (all icons and bolts on the flamers is a good start) and you'll be able to afford a greater daemon. Either a bloodthirster or a lord of change would be great choice and gives you anti-tank powers as well as a nice beefy combat unit.... and all the firepower you can draw into a GD will pull fire away from your troops (always good) since the enemy will target the flamers first, the GD second, probably bloodletters 3rd, chariots 4th and leave the horrors well alone... giving you lots of troops to play out the endgame (as well as having lots of bolts frying the enemy if you follow my advice).
