Originally Posted by rossrjensen 
About 4/5ths through the main quest, you are transported to a different map altogether. You can't go back to the original (much larger) world map.
Yeah, that caught me off guard, and I wish there had been some kind of warning beforehand. There were a few quests I hadn't completed in the other maps, but I didn't feel like going back to an earlier save by the time I realized it.
That final 1/5 should have been cut from the game entirely, imo.