Ouch... Looks like I called that wrong, Belugn. I thought that you would enjoy the battle system in XIII. Hehe... *sweats*

I honestly don't know where to begin in this topic. Lots of stuff have been covered so far, so I guess I'll just start with the main focus. High HP in enemies.

Wow... I don't think I've ever had to spend so much time in one battle as I have in this game, and most of it is just on the normal enemies. However, I do enjoy the more strategic aspect of what the Paradigm shifts offer for the player. It took a while to get used to, because I honestly am not that good at strategic battles (I used to just over power my characters in other games and beat them that way ), but once you get the hang of it, it's really fun. For me it is anyway. I like the Eidolon battles. You have to be really strategic to get that Gestalt mode bar up in under the set time limit so you can actually beat the thing.

I somewhat agree with the point made about SE feeling the need to give bosses ridiculous amounts of HP to add challenge. It does seem really just like a cop-out, but as stated previously, it's the Stagger bar that makes it sooo much fun. ^_^ Finding the right combination of paradigm shifts to get that bar up to max is something I find to be pretty fun about the battles in the game.

As for reward for going through these tough battles, I do find it a bit lacking as you stated in your OP. I've fought some battles that took a long time, and in the end my reward for doing it was less CP than I hoped, and next to no items for upgrading my stuff. That's honestly my only complaint so far with the game.

I haven't had any noticeable problems with my AI, so I haven't done any yelling (not that I could yell anyway =P). It could happen though, and I'm sort of counting on it to, because I'm not really even very far yet (started my game over), and I'm pretty sure that when I get to the more tougher battles, that my AI characters are going to not be there for me when I need them. I have plans to counteract their deficiency though, so I'll get back to you when I get that far and actually use my plan.

The Chrystarium is indeed linear at first, but once you get to the later levels of it, and have to decide what you want each character to focus on, it gets much more enjoyable, because you do have that bit of customization that made so many other games in the series that much more enjoyable. For me it did anyway.