After hours of work, I made it to the final dungeon, and took out the last few bosses, to complete Infinite Undiscovery for the first time. This is only the second JRPG on the 360 I've been able to play through all the way to the end of the story. Enchanted Arms would be the other.
I found the ending of IU to be very satisfying, and the last dungeon was a decent challenge. I nearly wiped out on the last boss twice, but I beat him without reading the guide's suggestions, which makes me happy.
Now, I've beginning the post-game achievement mop-up. I loaded older save files, netting the "On the Run" achievement on the first try, then I loaded up another save and earned "The Tide of Battle" on my 2nd try. With those older achievements now out of the way, I've been working on grinding up the IC levels of my party members, so I can craft many of the items I'm missing for the "Compulsive" achievement. I also need their crafting levels up to learn all songs, spells, and abilities, and obtain the achievements for crafting some ultimate items. I can get up to 939 in this playthrough before working on Hard.
I'm a long way from done with IU, but at least on the next to plays I can focus on the parts of the game I like, and not bother with the terrible sidequests anymore. IC grinding, unfortunately, will remain necessary to get the items needed to beat the game's ultimate boss. My gamerscore won't be going up very fast for a while, as I'm alternating between this and Sacred 2, which are both 100+ hour projects, and completions to be proud of.