Huh. That's interesting, because to my mind that same reward-system thing is precisely why it seems worse than a more linear time-per-level. When time between levels goes up, I find that I lose investment compared with when level-ups are more frequent, because I'm no longer getting the constant rush of Cool New Stuff to keep me focused. But I guess maybe I'm just psychologically weird in that regard and for most people the slower rate feels fine once they're hooked?