My personal one is Star Ocean 3, which is convenient to talk about because it's split into two defined halves: disc 1 and disc 2. To be honest, disc 1 is one of my favorite games of all time. Disc two though really goes downhill. The difficulty curve goes completely up the wall, with some enemies getting a long range, high damage attack which is hard to stop, impossible to block, homes in on you, and makes you stagger for 10 seconds so they can spam it (this is called a dick move, Square). Also, many enemies start attacking MP instead of/ as well as HP, which would be fine if it wasn't for the fact that if a character loses all their MP, they're knocked out, which made all of my tank characters fall like flies. Lastly, the final section is 3 or 4 straight dungeons with enemies that rapidly grow in level, with no places for healing or item restock on the way, unless you treck all the way back to the nearest town. There are about 3 bosses on the way with the two stage final boss at the end, and if you make it to the end with any of your healing items left it's because you managed to run from every single fight. I made half way through the final boss's second stage, but after my 8th attempt I just gave up on it as a lost cause.
Also, the plot of the second disc is just stupid, and what I found out about the ending was anti climactic and not worth what you went through to get to the end.