The most surprising thing to me is that I wasn't convinced they could achieved a visual wow when they had released the second movie ....

Oh man I was wrong there. Perfectionist directors can achieve impressive things sometimes ...

Probably lord of the rings

this

Before Hobbit/Lord of the Rings, which I've read in early 80s, before D&D which I started playing in mid 80s, watching Jason and the Argonauts for the first time in late 70s, and especially that scene, is THE thing that got me into that type of fantasy.

On topic, out of the older stuff, Star Wars.

Out of newer, practical/CGI combos like Lord of the Rings and Pirates of Caribbean (especially those with Davy Jones).

I’ll second the old Star Wars movies for their practical effects, Pirates of the Caribbean for Davy Jones and The Lord of the Rings. My favorite is that last one because of its blend between practical effects, make-up and prosthetics and CGI. A real masterpiece in all aspects. Even all-CGI things, even though this was made beginning 25 years ago still hold up perfectly well. Like the Balrog. And wideshots of the battles.

Yeah I was sceptical that the sequel could be as impressive as the first, but the way they absolutely nailed the interaction with water which is incredibly difficult to pull off in CG was incredible, not a single shot stood out as fake or overly artificial which was a real achievement given how trained our brains have become to picking out computer imagery. Crazy ambitious stuff and executed brilliantly. I look forward to seeing the third film continue to push the envelope.