OD&D
- Good: The entire concept, borrowed from the Braunstein game, of playing an individual with open options -- combined with magic and monsters.
- Bad: The rules. The good parts of the game didn't involve the rules.
- Ugly: The organization of the rules. There was no organization. And many of the rules weren't anywhere in the books. You were supposed to know they were somewhere in another game you were expected to own -- but not use in its entirety.
- Good: Lean presentation of a fairly simple system and a wonderful game concept. Shared experience of Keep on the Borderlands.
- Bad: The fairly simple system nonetheless constrained players for no good reason, with races as classes, etc.
- Ugly: The "basic" name and the game's incompatibility with the "advanced" version.
- Good: The original D&D books are full of evocative bits and long lists of (random) ideas for anything and everything. Shared experience of GDQ adventures.
- Bad: Most of the advanced rules made the game less fun, if you could even understand them.
- Ugly: Psionics. Pummeling.
- Good The campaign worlds: Dark Sun, Birthright, Al-Qadim, Ravenloft, etc.
- Bad: It could have been so much more. AD&D needed to move forward -- maybe not in the direction of other games, but it needed to move forward -- and it didn't.
- Ugly: Countless books of no real value.
- Good: The basic d20 framework, with its unified mechanics and flexible classes, like the Fighter with its Bonus Feat list. Shared experience of those first few modules.
- Bad: "Necessary" (and cost-effective) magic items.
- Ugly: Overcomplicated builds with races, classes, prestige classes, and feats lifted from dozens of books.
- Good: Martial characters are given interesting choices to make in combat.
- Bad: Long lists of game mechanics with mis-matched fluff.
- Ugly: Total abandonment of "simulationist" in-character rationale for many powers.