So I got to the Final Battle and began the ending sequence last night - but after reading a few things about possible romantic subplots, all the amazzzzing gear people say they were getting, etc I can't help but wonder - How the hell did I miss it? I basically ignored a lot of the "kill X" sidequests and stuck to the story missions. I skipped the grimoire and witch quests but that was about all I can remember ignoring.

Is there a mystery town or something that I overlooked besides Gran Soren?

You are not at the end of the game yet.

If it makes you feel better I'm on my second play through, and I'm finding areas that I never even knew existed.

I skipped the same quests you did and I think there were a couple more that I missed, then the way I hear my friends online talk about the game it sounds like those open up into even more quests that I missed. One of my friends just goes out and explores a lot so I think he is a getting a lot out of this game, but I'm too chicken to do it- especially now that I'm in the "post game" or whatever.