I've been playing the game and I liked it a lot. I have beaten the level 10 (after losing some characters) and then I started again. Now I can give you some ideas that I think they could improve your game, maybe some of them are usefull for you:
The HUD messes with the gameplay when your character explores the edges of the map. To avoid this, you could:
· Generate the unbreakable bricks some pixels away from the borders of your layout. You can start your map on Y = 100 and finish it on Y = (max Y) - 100, and move the info about the enemies remaining to the center of the screen.
· Make an event to set invisible some specific info in the HUD when the player aproaches an edge. You can make a smooth transition by reducing and increasing its opacity if the character gets closer or farther, for example.
More than different graphics, it would be funnier to fight different skilled enemies. Some examples could be:
· Shielded enemy: unlikely an armored one, this reduces a lot the damage received from a certain angle. You can make him turn slowly so the player wants to move to its back to shoot it.
· Magic shielded enemy: this one could work in different ways.
* It has its shield active for some time, then it deactivates (just once, some times, forever).
* Its shield could absorb some damage, then it dissapears (and stuns the enemy, for example).
* An enemy is shielded by another static enemy, which just concentrates on shielding his ally and must be killed first.
* The shield could reflect the shoots from the player randomly, and maybe towards the player on higher levels.
· Warping enemy: it warps randomly to an adjacent tile (to avoid moving it to different rooms and making the player to initiate a boring chase). It could warp behind the player at higher levels.
· Explosive enemy: it explodes when killed (or when it attacks). It could even break adjacent bricks.
I like the way the player can interact with the map, but it's only ground and walls. You could add:
· Lava ground, to hurt (or instakill) the player. You can even make it hurt the enemies and add some enemies invulnerable to lava.
· Glue ground, to reduce the speed to anyone over it. You could make some hovering enemy inmune to this efect, and even an artifact for the player.
· Ice ground, to reduce deceleration to anyone over it. You could make fireballs to melt the ice (just delete the ice after some short animation).
I haven't checked this, but I think a level can actually spawn more chests than keys. It's disgustin for a player to find a chest and not be able to open it even after exploring everything and killing everyone, so you could first spawn keys around the map (both on the ground and on enemies) and then spawn a random number of chests with a max value equal to the keys the player has plus the keys the map has. Buying more keys from the shop would increase the chance of finding more chests, changing its functionality.
I hope this helps you.