When are you going to include more vocabulary? In the other languages going up levels includes more vocabulary. In this version it spreads that there is no need to continue up levels because it's just repeating the same 4 words or phrases over and over again. It's becoming boring, and that's not good!
I actually wouldnt want higher levels to include different words. I wanna have some time between doing the different levels so i dont just remember everything cuz i did the same stuff the day before. But once im at level 2 or 3 i usually proceed to the next skill. But if id need words for that which were only introduced in level 4 or 5 that would only lead to confusion and frustration on my side :D