First at all, Kingdom Rush Frontiers is a challenging, funny, and well balanced game so improving it is not an easy task. I'm assuming that you're asking about improvements, not adding content (if you like the game, longer campaign and more heroes can be an improvement).
- Objectifying: when player faces a map where he/she has been defeated, the player needs a way to get better. Why have I lost? Which ones were my errors? How can I avoid repeating them? One of the best ways of doing it is objectifying the player performance or what exactly happened during the round.
E.g. you lose on a map and a screen let you see how much damaged have you done, which type of enemies healed themselves, which ones went through your defenses... a game that has a great (but not perfect) system to do this is League of Legends. After a match ends, you can see some statistics that let you know accurately what happened.
Creating this kind of system let the players now about his/her performance and creates a simple way to improve.
- Perceived imbalance: one of the lateral problems that are related to the lack of objectifying is the perceived imbalance. Imagine this: you try the game for the first time, you have your first hero (Alric) and after some rounds you have some coins to spend. You read carefully every ability because you now that coins are really hard to get and you find this: "Sand Warriors III: summons three sand warriors with 140 life each" Is easy to think "Ehhh... 3 warriors? 140 hp each? My hero has 300 hp! That's the best ability ever!!!!"
Of course a game has to be balanced (KRF is well balanced) but it has to show it or the perceived imbalance is going to push the players to the get the ability/object as if that was the last thing that could they ever make in their lifes. Fighting the perceived imbalance is not an easy task but some of the main techniques, aside from objectifying, are informing the player about alternatives or rewarding the player for choosing different alternatives.
- Making spending money an attractive task: I love games and spending money on them is something I like, but for doing this I need to know what I'm buying. KRF has a problem here: the main way of spending money is buying heroes, but I don't know what exactly I'm buying. How can Ironhide Game Studios make this task more attractive? Showing me the heroes. A small video, some screenshots of the abilities... whatever it is that makes my hype grow!
- Minor improvements: some minor details can improve the game easily:
- How exactly does the player win stars? (15 or more life points at the end means 3 stars, 10 or more life points at the end means 2 stars...)
- Health bars with different colors for friendly units and enemy units, this way the player can see if he/she is winning or losing the battle easily.
- Hero radius of action. Showing the limits of the heroes activation range can make it easier to place them.
Hope that was what you're searching for with your question.
