One of my favourite LEGO MOCs ("My Own Creation" although this one isn't my creation) I've seen has been Iggy Pop and Tom Waits from the movie Coffee and Cigarettes:

https://bricknerd.com/home/cigarettes-and-coffee-man-thats-a...

https://singersincinema.wordpress.com/wp-content/uploads/201...

There's some plans out there for fantastically detailed models with thousands of pieces, for instance The Sulaco from the movie Aliens: https://www.reddit.com/r/LV426/comments/vs6b1x/as_promisedth... (that one is definitely a lottery-win purchase!)