Well first of all, I never get into a position where enemies are behind me, which seems to be one of your main complaints. The blocking mechanic in TW2 uses your stamina points (that's why you got hit while blocking, your stamina was probably empty), so I usually just dodge roll instead of blocking to get into a good position, and then use whatever attack is effective in the situation. I played it on hard difficulty and never had much of a problem.

Yes you do. There have been times when enemies have been on the side or behind you. It's just not possible for that not to happen.
Another reason that makes me think this is b/c I never said I'm getting hit while blocking. So you're conjuring things up to give the illusion that I'm playing the game wrong. Not necessarily on purpose.
If I'm attacking 3 guys and I attack one guy theres going to be one guy that gets to the side of me at the very least. If I'm facing North and the guy is on the SW end of me and I press the "A" key to attack him next, my guy will attack thin air instead of facing the guy on the SW end of me. With the way Garrett runs and how the mechanics of the combat are, it needs to work like this. If I was to press the the "S" and the "A" button to turn SW, Garrett doesn't turn his body...he like runs around or some [censored]. It's just odd...the targeting is off. If I roll into combat, strike once and try to roll out, the controls are so unresponsive that sometimes A) the second roll is delayed....or B ) the roll just doesn't happen.
The enemies with shield need to be blocked first to stagger then attacked. But if theres 2 other enemies and I'm trying to block that one guy, I get hit by one of the others from the side, b/c my block has to be directly facing the second guy. While the facing part sounds "realistic" or whatnot, it creates a problem. Theres no way of attacking the weaker guy with the shield and taking him down before the big guy. So instead of using common sense to take out easy opponents first, I have to run around like a [censored] dodging attacks trying to get them lined up > big guy then shield guy.
Thats not fun. I did that back in the SNES days and it wasn't fun then. If I could play the game and tell you these things as they were happening the explanation would be more clear.