At first this may seem to be a largely opinion-based question, but the more that I read the more that there appears to be a consensus. For example, in something resembling decreasing order of the frequency that I’ve seen these claims, the following appear to be commonly believed:
- Any content focused on Epic level gameplay, such as the Epic Level Handbook or Deities & Demigods, should be banned from player use. The reasons for this vary, but I usually see either poor editing, completely lack of balance, or complete lack of thought listed as reasons. The best example is Epic Spellcasting and its numerous dysfunctions, although I could also point to absurdities like the lack of balance between Saleient Divine Abilities (even in the hands of NPCs) or Boccob only having two classes.
- Serpent Kingdoms is so poorly written and so exploitable that it should be ignored. For example, see “GeneralCategories” (sic) here or recall Pun-pun.
- Unless you don’t like the flavor or one or two feats that cause ruling debates, the Expanded Psionics Handbook and the Tome of Battle are some of the best 3.5e books.
- The Book of Exalted Deeds largely contains material that was originally made for NPCs and some of it, particularly anything that requires the Sacred Vow feat, is dangerous to include in your game and may even damage your group. Vow of Poverty is an excellent example, along with the Apostle of Peace.
To me, this list is evidence that some consensus exists on which books should be banned due to either exploitability, lack of balance, or poor editing. My question is this – aside from the examples listed above, what other consensuses exist and what is the reasoning behind them? To be clear, I’m only looking for information on what non-third party books should be banned entirely. I don’t care too much for anything like “be careful what you use from Unearthed Arcana and Dragon Magazine“, “the PHB has poor class balance”, or “don’t allow Domain Wizard”. I just want to know what entire books are frequently forbidden and why.