So what changes to core D&Disms (classes, mechanics, settings, meta-game, etc) that have occurred over time do you like? Which ones could you do without?
Classes: I have a like/dislike relationship with addition of core classes, especially when they work so hard to balance them. When playing D&D, there is a side of me that likes classes to fill a role. But, there is also a side as a player that says, "It's awesome that I am the cleric and not the only one that can heal."
Species: In a D&D game that is set in the FR, bring on the cantina. It's fun and enjoyable. It's Star Wars mixed with a touch of Lord of the Rings. A fantasy encyclopedia inside the New England Journal of Medicine. And I am here for it. In a D&D game in other settings, it feels terrible and wrong and sacrilegious.
Settings: I like what they have done to the settings. I even liked the lore dump for 4e. I don't think it conveyed it very well, but it worked for me and my players.
Mechanics: I appreciate 5e - a lot. I like the feel of its play. I like its ruleset. I like its balance. I dislike combat after 8th level because of its length. I liked 4e. I liked the whole powers being encounter, daily, utility, etc. I liked its ruleset. I thought the balance was a little too good, and that made the feel a little too structured. I disliked combat after 5th level because of its length. During my limited exposure to 3e, I liked it. I like the options. The ruleset. The feel was fun. I disliked combat at all levels because of its length. I liked 2e - a lot. I liked that classes had roles. I liked the ruleset. I thought the feel was a little lopsided at times. I liked combat, but we were also able to play 12-hour sessions until 4AM. So... rose-colored glasses. I liked AD&D - a lot. I doubt I knew enough of any ruleset to judge. But middle school wouldn't have been the same without it!
Meta-Game: I like the addition of session zero. I like the continual shift to inclusivity. I like the extra space given to player-focused campaigns. And like most things, the pendulum always has a way of swinging too far one way making the other side look lopsided.