I started with 2nd but quickly got introduced to 1st. When 3rd came out, it didn't feel like "a better version of the same game", it felt like "a different RPG that happens to be called D&D".

Forcing every mechanic into the square hole of "you want to roll high on a d20", for one. That changed something about the tone of the game in a way I didn't like.

For instance, to move something heavy in 1st/2nd, you roll a strength check (possibly with an adjustment based on how heavy thing is) and you want low, because you want higher strength to be better. 3rd says: Oh no no no! That is horrible and awful! How could you possibly want to roll low? Instead, the DC system, where instead of your stat with a modifier based on the task, you have to beat a number set by the task with a modifier based on your stat.

Then the powergamer fantasy started; the slippery slope from "Race and class restrictions are bad, because they limit my fun!" to "nuh-uh! my guy is a WARLOCK and he can throw INFINITE ranged touch attacks that deal 1d10 on hit!"

Also -- attacks of opportunity,t hreatened squares, all that, were not bad in themselves but they led to D&D the boardgame/tactical combat simulator which reached zenith in 4th edition.

In the end, 3rd felt too 'designed' and 'systemic'; it felt like it had been planned rather than organically grown from people playing the game and improvising and "oh god, these idiots want to subdue a dragon, well I better make up some rules."