it's listed in the FAQ, but i use godot for this! it's a free engine, and how hard it is to learn/navigate is going to vary wildly based on your previous experience, i'm a programmer by trade so i had a significant head start. i really like using it though, it's an especially nice fit for pixel art in my opinion.
thank you for the kind words! i'm excited to get to work on it more when i can :)