I finished the main story the other day. Took me right at 100 hours. I was getting real burned out at the end, I should have paced myself more. What really got to me, though, was trying to high score all the mini games. I should have put that off until after I beat the game. I ended up giving up on that goal (which was not a smart goal in the first place), and maybe I'll try later. The Ultimate Party Animal quest is still bugged for me (and a lot of other people) and there's no indication it will get fixed soon.
The chapter select unlocks after you beat the game, and it seems pretty easy to jump around and complete stuff you left. I wish I had known that ahead of time.
I enjoy a lot of the mini games, but some don't click with me and some get ridiculously hard. The 3d brawler is awful and the Chocobo Glide game was not fun at all for me, just to name a few.
I LOVED the game, up until about Chapter 12 and the burn out set in. I was trying to do all the side content/mini games and I really didn't need to cram it all in. Plus, the boss gauntlet at the end of Ch 12 was...not fun. That boss at the end was such a stark difference from everything else in the game that it threw me off. The boss could track me through my dodges, and that felt awful. But after Ch 12, and deciding to put the mini games to the side, I finished up the game and was blown away. The ending had a lot going on, a lot to process, but it was a hell of a ride.
Anyway, overall it's a great game. Jam packed with content, made with care and lots of attention to detail. Getting the Plat trophy seems like a real stretch for me. I want to, but the time and skill required is daunting. The combat simulator fights look like they might be beyond me (and I'm no stranger to FromSoftware games).