Thats exactly the reason why i supposed to work out a concept first. Even multiple survival maps, although they look similar, are not really compareable. E.g. enfos is more competative orientated, with clear vision of whats going on on both teams and what happens next. Item Progression brings up power spikes with sometimes ridiculous stats. X hero siege on the otger habd is more deceptuvw, with maby supruses while you are fighting the waves (and dont let me begin on the end part). Custom hero survivalputs its focus on the hero progression by customizing your hero by picking skills. Notd aftermath goeas a completely different way, putting the whole setting into a zombie survival setting and encourage going through the whole open map for evading/objectives/supplies. I am myself creating a survival map which is build completely different than these (Invasion on Az'kar)
Overall, you need a proper idea before you can get toughtout feedback. But i can give you an advice on what can be quite important:
Polishing
Many survival maps are very unpolished with missing tooltips, green icons, random looking or blank terrain, blank items, non synergistic heroes, random enemies or sloppy triggers. You can go a long way of highlighting your survival map among others by just polishing it.
On the other hands, there are like, what i would say, traps for survival maps (some of these are overall mapping pitfalls):
-too many enemies: well, we all know how awesome it feels to pludge trough a great mass of enemies at once. But once your screen is filled with enemies and the game starts lagging because of pathfinding problens, you should thibk if you have probably overdone yourself. The amount of units on a map affects balancing either. This is a reason why cleave is a sought after ability in many survivals.
-useless skills: its a balancong issue, but one that is directly arising to a player. When there is that one skill you dont want invest into until you maxed everything else, you should ask why this hero still has it. If you come up with an idea to make it situational usefull, go for it. That AOE manaburn ability could surely have helped against that pesky casters last round.
-Tomes and too much gold: Always be aware that when you wamt to add tomes into your map, you are removibg the power ceiling. Even at max lvl and full slotted, ppl will still progress in power, making balancing for the endgame a hell of a task. This is one of the reaso s why many surival games are missing dedicated supports. There are plenty of recouces on the map, you can gi for the right clicker wuthout hurting the team as a whole.
- hidden recipes. Nothing infuriates more than having recipes that one has to find out by sheer trying andexperience. No, you wont find the combibation of 3 itens among 45. The only exception is if you want some kind of easter egg or a riddle.