NIce Game, got medals, upgrades, nice concept, nice story no real flaws, but for that last star, you'd need to do a little extra:
-make it possible to see your stats (distance and flawless time) during the game (if you're afraid this may be stressful for some players, make it something which you can turn on/off)
-make it possible to see your personal bests (distance and flawless time) trough the main screen
-get the medals as newgrounds medals
if you improve at least 1 of the above, I'd make it a 4.5, if you manage to improve all, I'l give a 5
oh, and one last idea, which doesn't affect my rating, but I think it might be nice:
add usable items, such as life potions (gain x amount of health/restore full health,) strength potion (don't loose any health for x seconds), magical sword (beat the next x amount of animals you encounter), and/or money magnet (attract money near you for x seconds) (and perhaps you might have more ideas yourself)
this is especially nice if you've got all updates already, and you have money which you can't spend, but with this, you can buy items
then you should be able to activate the items using keyboard keys (e.g. 1, 2 , 3 , 4, or v, b, n, m, or anything the user wants, really)