3. Phantasy Star II
Even with the hint book that it came with, that game was f'ing HARD!
The Bard's Tale games for the old Commodore 64 were hard as hell, too. Not the game itself, but the fact that they had no auto-mapping feature, which meant that in order to map out those pesky dungeons, it was just you, a book of graph paper, a pencil, and plenty of free time on the weekends!