Pretty interesting idea on the mix of 2048 + tower defense! A few opportunities that I see:
1. Overall there're a lot things going on, and not a lot of explanation for them. I almost bailed out for not understanding what's going on
2. The level up mechanism, which is very important, is not explained in game (afaik)
3. I couldn't find how many units I could spawn with the current houses I had, or how many units each new house allows (I saw the x/y later on the units count)
4. I wasn't clear on how to spawn units at first
5. The difficulty ramp up seemed pretty insane to me
I do think you have a cool idea here, and the assets you've used fit pretty well, just needs a gentler ramp up and some polishing imo. Well done!