It looks to me like the graphics are better, but I haven't actually played the game.

"Mission Complete" might refer to the additional experience points you get for completing a scenario. At least, that's how I think it goes. You also get EXP at the end of the fight, as you normally would, but you get more upon completing the mission. Again, I haven't played the game yet, so I'm not a 100% sure about these things.

Final Fantasy X-2 having its own forum, hmm? Maybe after the US release.