What are the major differences between AD&D and D&D 3.5e?

Question

What are the major differences between Advanced Dungeons & Dragons and D&D 3.5e? My DM is used to old school D&D and wants to know the differences.

Answer 1

The source materials from AD&D 1e can quite often be used in AD&D 2e with little or no changes. Especially monsters or modules.

The sources from 2e are, mechanically, not useful in 3e or 3.5e. The shift from THAC0 to the D20 core engine "breaks" basically everything in 2e.

• High ACs are now better than low.
• High Saving throws are better than low.
  • The old PPD, BW, etc. saving throws are gone. Now its based on the stat used to defend.
• Strength no longer has the old 18/00 sub-setting.
  • Now all stats range from 1 to infinity, with modifiers that go up as the stat goes up
  • Now characters increase their stats over time
• The classes are heavily modified
  • No race/class combination restrictions or racial level limits
  • Paladins don't have to serve a god; they can serve an order/oath instead
  • The blue and red books of core class "kits" no longer apply. Though classes are just as easily tweaked towards or away from vanilla versions.
• Feats (special abilities that aren't magic but are outside the reach of mere normal folk) are all new
• Skills are heavily revised
  • Take 10 and Take 20 options allow for "always pass" skill checks
• Prestige classes are all new
• Core rule gods are new
• Spells/psionic powers are different in various places and ways
• The rules are more solid about how to create (as opposed to just find) magic items.
• The list of classes in the core rules of 2 and 3 are not identical
• Costs for non-magical and magical items have changed
• The races have changed
• The monsters have changed mechanically
• Many of the 2e setting boxed sets never received official 3.x edition updates (though the internet has many helpful resources for this gap)
• The way XP is figured for encounters has changed
• Class progression, multiclassing, etc. have all changed
• Many combat abilities, along with the combat rules themselves, push towards the use of miniatures. Gone are the 2e days of "buy the weapon with the biggest damage die and attack until they fall."

Basically, almost none of the rules in 2e are handled the same in 3e. The official "how to transfer your characters from 2 to 3" guide basically boiled down to (if memory serves):

1. Decide if you care more about matching abilities or class levels
   1. If abilities, then find the new classes and levels that correspond to what you can do in 2e. Rewrite your PC at that new class/level.
   2. If levels, then create a new character of that class/level.
2. Ret-con away the sometimes-radical changes in what your shiny new PC can do vs. what your old PC could do.

(I would prefer to close out an ongoing campaign in 2e, then start 3x with a fresh, new, campaign, rather than convert over. But that's a personal opinion.)

And just enough changed in the jump from 3e to 3.5e to break at least some of the supporting material all over again. Modules are still okay, and settings books. But the core classes and spells were tweaked quite a bit between 3 and 3.5, such that the expansion books for classes in 3.0 are not mechanically "plug and play" compatible with 3.5.

Answer 2

The big shift from AD&D2E to 3E is the adoptions of Wizards of the Coast's D20 system. In 2E, every game mechanic (thieving, attacking, proficiencies, etc.) had a unique set of rules. Now it's all simplified to a d20 roll + modifiers versus a difficulty class determined by the DM.

The best example of this is the loss of the THAC0 system and the inversion of AC scores. In 2E, an attack roll was like this:

1. Roll a D20.
2. Add the enemy's armor class to your roll.
3. Try to meet or exceed your THAC0 score.

It's an arbitrary system that results in lower numbers being better.

In 3E, a combat roll is just like any other roll:

1. Roll a D20.
2. Add your base attack bonus to your role.
3. Try to meet or exceed the enemy's armor class.