Concept's pretty great. The pixel art graphics are gorgeous and the music was used quite nicely.
Does seem pretty weird that the names become normal names with letters added, though. The difficulty is fairly random because of that since you could get two of the same letters in a row, or two letters on the complete opposite side of the keyboard.
I'm gonna have to agree with one of the earlier comments saying all names should be real ones, though, with the name length/difficulty increasing every time you kill X number of heroes.
Still, pretty fun game, definitely needs some expansion.