Which PC games played differently at launch VS with the latest patch? What changes do you remember?

The best example I can think of regarding this, is the original Far Cry by CryTek. I still have an old Windows 2000 machine to play the vanilla retail version with, free from any glitches of newer hardware, and the enemy A.I. is significantly less aggravating in the unpatched version than when you download the same game from any modern online service (i.e. Steam). I don't exactly know what happened after patching this game, but now it seems the "intelligent" enemies the game envisioned have been mutated into demigods who thrive on defying the laws of physics.

Are there any other games like this you remember, where a later patched changed something noticeable of how the launch version played? If so, what were the changes?

There are many games that release broken and later get fixed. Also, there are many live service games that change quite a bit like Destiny, The Division, Anthem, Battlefield, Warframe, etc.. However, major changes to a product that was supposed to be complete.... Dying Light changed quite a bit and was re-released as Dying Light: The Following. I remember they reworked the inventory and loot management in The Witcher 3. Mass Effect 3 ending rework.