Just leveled up my Barbarian (who I think absolutely rocks btw). It says I can increase HP by just 5 points, so I was going to increase my Barbarian from 3 to 5 hits on the first level up! It wouldn't let me though, so I'm assuming that it's suppose to read as 15 points to do so (which I would agree with).
So instead, I was able to level him up to 50 Strength. I have a 50 strength, 3 HP unit roaming around in like the 6th turn of the game, how sweet is that? I'm thinking it might be too sweet, but we'll see!
By level 4 I'll have a 60 strength, 4 HP unit.