I was going to post about it when i saw this topic. The idea of having "squares" (1 square = 100hp ?) is very good, you can estimate the absolute (ie. not relative) amount of hp a champion has. But as said, this doesn't work with 4000+ hp :
On this screen I just died because the bar was so dark I thought Allistar was nearly dead and ran into him.
Maybe you should increase bar size when hp are too big so we can still see the "squares". Or display two lines. (or both)