Okay, I tested it out, and it's pretty cool! Good job with the map!
Some heroes felt a lot better than others, such as Lich. (Frost Nova seems to be really strong for a level 1 spell compared to all of the other heroes, and levels 1-4 seem to be the ones that matter most for heroes.
You have a wide variety of towers, and that's pretty cool. They all feel quite unique too.
I like how towers can have items, but sometimes the items can get really overbearing, like the powerspike the Rapid-Fire/Barrage tower gets from getting its first Ultran Blade. I feel like that is a really strong combination, perhaps too strong.
I like how you have the three different options that stem from the non-combat tower, but because bases are so big, I feel like you could have more, along with bigger buildings. Bases feel pretty bland when I look beyond the combat towers. It's like I have 20 gold generators, a unit production facility I'll never use, and three level 3 shops for fast Ultran Blade buying (since that seems to have the largest effect on the survivability of your base for its accessibility and price). The bases seem so large too, like I'll never run out of space even if I place stuff stupidly. The original Fortress Survival didn't have that feeling.
That said, the terraining is good though. It's pleasing to the eye and also mechanically well constructed.
One thing I found was that the Visibility Dummy was selectable and could build stuff. If you give it locust that should fix both of those issues.
I think that some of your build times (in the tooltips) for the Gold Mines are off, the first Gold Mine definitely doesn't take ten seconds to build (at least with a fast game speed, which is default).
Also, instead of telling us how much gold we get every thirty seconds, tell us how much gold we get every income tick (which is I think every five seconds). This is for clarity's sake.
Also, it takes a slightly longer than preferable time for the scoreboard to update the income increases or decreases for built or destroyed gold generators.
The enemies seem to ignore the base directly southeast of the Dark Portal for an extremely long time unless they somehow get vision of it. I haven't seen this occur for any other bases, but I've only tried a couple.
The Transmute ability is cool, but it rarely sees use because gold generators tend to get put in the back of bases and are not in range to turn anything to gold, unless an air unit comes from behind. A range increase, or perhaps changing the ability to something else, would be nice.
Tower fusion is really cool. Are those all of the tower recipes, or are there secret ones? (Adding secret recipes would be a really good way to get players to replay your map, if you haven't done that already.)
Your multiboard is informative and concise, and that's good. It's also nice that it has icons.
Overall, great job though. I enjoyed the map, although it is a bit hard.
(I guess I lied about not giving it a huge review.)