I singled out ELH over random terrible 3PP because I've actually put time into trying to bash ELH into something that even kind of works, while most bad 3PP products barely register with me enough for me to remember their names.I'm surprised that the Epic Level Handbook is the worst book for so many people. I thought I would be alone in that being people's worst books, especially given how many horrible 3rd party books were released during the 3.0E era (looking at you Fast Forward Entertainment!). Thankfully I was wise enough at the time to not actually buy any of those books.
In undergrad, one or two of the campus houses and maybe the TTRPG club had these boxes of supplements that had been donated mostly by graduating students over time that were sort of community property, and while some of it was okay, a lot of it was some of the most confusing nonsense that I'd ever seen. I'm not even talking so-bad-it's-good; I'm talking just, like, mishmashes of AD&D and 3e/3.5 stats and presentation in the same product, references to non-existent action types, new made-up bonus types for every bonus (A +2 Greater Seelie bonus to AC! A +4 Titania's Favor bonus to Bluff and Persuasion, which is presumably supposed to be Diplomacy or something?), that kind of stuff. I'm pretty sure that at least one of the box benefactors really, really liked fae stuff, because that sort of material was not only overrepresented (although to be fair, that was a pretty common well for 3PP to go to in general), but seemed to have the least quality control. I'm pretty sure you could have an entire fairly large party made up of people playing different takes on a stock Faerie PC race just using stuff from those books. And they'd almost all have at least one confusing ability that doesn't work quite right or be just hilariously unbalanced for a LA+0 PC race, or else "balanced" with infuriating RP things. Lots of trademark 3PP nonstandard templating, that sort of thing.