I know I'm going to be in the minority, but I was really disappointed. I was a Playstation fanboy and I bought an original Xbox around the time of the 360 launch since they sold out as fast as they were delivered. I figured there would be plenty of exclusives I could play for cheap. IGN was gospel to me at the time and it was their highest rated Xbox game so I bought it along with the console.
The biggest complaints I remember having were:
Voice casting: It appeared they hired voice actors from Hollywood classified. Everyone did a fine job, it's just they didn't sound Asian. I read the credits and found some Asian names, but what's the point if they speak like George Takei or Connie Chung? I hope I don't come off sounding insensitive and I definitely don't want to hear stereotypical voices, but the Eastern dialects have a certain cadence and accent that was missing. It's a shame to go through great lengths to make it look mystical and Asian and dropping the ball by making it sound Western. Brian Doyle Murray as the mob boss? Who casted him? I love John Cleese as well but thought his voice didn't fit the character either.
Conversation dialog: It seemed Bioware was so proud of their writing that every conversion went on and on with frivolous nonsense. This was before the hand holding map markers so a lot of quest information was in the dialog alone. It could be skipped, but a crucial bit was likely at the end of a long winded paragraph. If I missed something or forgot after a break I'd have to go through the whole conversation again. Many times I didn't want to hear the NPC's backstory or I how they felt about the situation, just tell me where to go and who to kill! Sure I understand lore and atmosphere and I do love that but this could have been better with a "fast track Cliffs notes" option in the dialog tree.
The looping character animation: This is a small gripe. I am already annoyed by the drawn out conversation system so this gives me plenty of time to notice the characters I'm speaking to look-left, look-right, look-left, look-right, scratch neck, repeat. I'm already struggling to pay attention and I'm constantly distracted by everybody scratching.
Combat system: I didn't think it was very deep at all. The fights I remember having were all won by quick jabbing. The stronger slower punches left me open to attack and there wasn't any reason to change styles. I only did so to keep me from getting bored.
I had a great time with Knights of the Old Republic and I really wanted to like Jade Empire. Perhaps my expectations were set too high from the glowing reviews. I put it down after 15 hours or so and walked away sorely disappointed.