The World of Darkness Books I bought (Vampire, Werewolf, Dark Ages Vampire - all pre-nWoD). I mined them for ideas, but the system and pretentiousness was a turn-off.
The Scarred Lands books I bought with the exception of the Divine and the Defeated. The early releases of the series just screamed "COOL" to me and I really loved the whole gods vs. titans take on the cosmology. I waited in anticipation for the Ghelspad hardcover and then started poring through the books to create my campaign....
...and discovered the holes, warts, and flaws of the setting that seemed to grow with each subsequent release.
Now I'm not saying the books I bought weren't good. Many of them were. I just grew tired of reading and thinking, so much wasted potential as different authors tweaked the backstory/history to account for their changes, or rewrote the things that made Scarn cool in order to conform more to traditional D&D. Great concepts, often poor execution. (High Elves, Termana, Psionics-for-Slarecians-only -- No wait, we changed our minds, etc. Considering I'll never run a game in Scarn, that's a lot of money I dumped into the setting.
Forgotten Realms. I shifted to the setting when I was too young to realize that publisher support isn't always a good thing - too many cooks in the kitchen making a big pile of yeah-it's-got-the-kitchen-sink crap. Stirring in uber-NPCs whose power would nerf your PCs ability to significantly impact the setting created a worse "what's left?" feeling than DragonLance or Middle-Earth did for my groups (again this was when I was too stupid to chuck the crap, but in looking back, I don't want to have to perform surgery on a published setting with a meat cleaver...) If only I could get the money back and have spend it on cooler product lines...