In general I'm a fan of FF, but XIII really disappointed me. Perhaps even more than VIII, and that's a pretty amazing feat.
Similar opinions here, I disliked VIII's monster leveling but its nothing compared to XIII. Luckily I bought it only recently when it was available for really cheap, and got enough enjoyment that I don't regret the purchase.
Some suggestions to get you thru the game (and hopefully enjoy it a bit):
1. Think of it as a tech demo for graphics & the battle system: I liked both of these, the actual ingame CG is even more impressive than the cutscenes imho (since it has to be done in realtime)
2. Skip all cutscenes with Vanille for first few chapters (say upto 8 or so), I didn't and regret that :p
3. Later on, Vanille becomes tolerable but Snow & Hope start getting extra preachy, so you might want to skip those scenes.
4. Don't bother with training or leveling up before Chapter 11 (Gran Pulse), just enjoy your tunnel ride with occasional looking around for treasure chests in obvious locations.
5. Consider having savegames before each cutscene so you can watch those again, we don't even get a cutscene menu after game completion :(.
As for 'what happened', I've read that partly it is due to the xbox space limitations - which does make sense, else not including the Japanese voices on PS3 bluray version is quite inane (but I'm sure they didn't want to highlight the space issues by differentiating it from 360 version).
It is actually a good game as a tech demo of the crystal tools engine, with a decent battle system (the paradigms are a good concept, not a big fan of crystarium though). Just don't confuse it with an actual RPG lol, let alone something of the scope of other FF titles.