Thanks for playing, Nick! Glad you enjoyed it.
The levels are actually numbered, it's just hard to see the numbers on the sprites (the color of the number and the background blend together). Originally you were supposed to unlock levels as you went with branching paths (with two levels beaten you can either go to Lv. 3 or 4), but that didn't make it in this build. I'll re-add this feature and make the numbering clearer in an update :)