You had me with the description... because of that I wanted to give you a quick overview of the map.
Still, multi-upload deserves some -rep (you've been warned twice I believe?)
Next multi-upload is an infraction
Terrain:
The terrain isn't exactly good: you'd have to be a good terrainer to let two opposited (here fire and ice) fit well together.
Bridges are rarely a good idea to place on places you
know many units have to pass.
Those bridges make the ground pathing a nightmare for anyone who wishes to retreat (or even attack) without failing too hard.
The thing that bothered me the most (probably) are the cinematic doodads.
I always say that you have to avoid cinematic doodads, I know that some people use them in a good way, but if you're new or not that experienced with terrain, it'll nearly always end up like this: a spam of flashy models.
So just remove the lightning and different fires for the time being.
Triggers:
Not much to say here... you've got memory leaks and they could be far more efficient.
I highly suggest you learn how to remove leaks, and eventually you may learn how to make your triggers more efficient as well (the leaks are more important though).
Objects:
As important as it may be, I'm going to keep this one short as well (in comparison with its importance, that is.
You've got some semi-standard items and ditto spells for heroes that look really good, but don't differ from regular heroes that much.
My advice: make more item abilities (may seem useless, but more item abilities means more possible item combinations) and, a more important hint: EDIT your heroes and spells!
Don't just copy/paste the standard ones, change HP a little, damage a little and done.
You've got to change a lot more values, balance them as much as you can (spells included), make them actually
be customized instead of only looking custom.
The more newbie players will indeed only notice the models, but for those who have played warcraft for a bit longer, heroes like that are not entertaining at all.