Two things should be said about
Armor Class. First, as of
3rd Edition, it goes up now (
thank you!). Second, though the
language used confuses this, it's been
officially said that
AC isn't meant to show how hard you are to hit; it's supposed to show how hard it is to land a
hit that actually
hurts you. Sure, you're still
technically hit if someone
clubs you in the
back while you're wearing
full plate, but...
I will grant that AC isn't the most realistic mechanic in the world. However, it is fast and simple, so if I were running a D&D game, that isn't one of the rules I'd try to rework.