I'm really enjoying this game, but something that is is missing (in my opinion) is a much shorter gameplay loop. The story missions are fun, and clearly the core of the gameplay, but as you get no rewards if you don't finish the mission, I'd love a shorter game mode to be able to quickly jump into if I only have 15 minutes or so to play.

My suggestion would be a wave defence mode. I would take the tutorial tower area, and turn that into a wave based mode. Waves would get increasingly difficult and every 5th wave or so could be a mini-boss (maybe add in dungeon bosses at high levels too). You could even add campfires at each 10th wave, giving the players an option to skip for loot increases, or refill their potions. The key aspect is that you can quit AT ANY TIME and you keep everything earnt from the completed waves.

I would suggest that clearing waves would only reward gold, XP and crystals, so loot can still be core to the missions, but this would provide a way to play quickly and still be rewarded for your time.

These mode could also be a decent end-game grind, peopel setting high scores or maybe there are 'themed' wave defences, leading up to dungeon bosses. If the idea catches on then even adding loot drops past the higher levels could be a fun thing to add.

I still think the story missions are the key way to play, but I'm just looking for a way to enjoy the game when I can't commit to grinding through some of the longer story missions.