I think a game that has a balanced difficulty would be what I would like the most. I mean, imo TD was cool because you weren't "forced" to abuse some sort of game mechanism like DDC's bomb, LOLK's life, UFOS'...ufo. I mean, okay, you could play those games on hard, sure but you can hardly 1CC them on luna without spamming the game mechanisms. It's not new, actually it was already the case with PCB and the supernatural border, but it was less active and clearing the game on luna without supernatural border is not impossible.
I love MS, EOSD and SA because you mostly have to rely on your skills and memory of the paterns, not game mechanisms.