Sims 2 isn't really all that "outdated" in its looks, with a little help from CC. It can look really incredible.
My friend Mortia plays a medieval game, and she has some truly beautiful pictures in this thread - https://forums.thesims.com/en_US/discussion/915458/the-kingdom-of-dallubach/p1
There are some other shots floating around of a sea, sky and pond overhaul for TS2 and the game looks amazingly realistic. I can't find them right now though; there was a thread in the TS2 section about it at one point.
I think TS2 is still the best of them all. I play both 2 & 3 but for different reasons. 3 is nice when I just want to play a single sim running around collecting, or traveling. I play 2 when I want to play large, fun families. TS2 always looks like it was made by people who really cared what they were doing, and wanted to bring the best experience possible, especially with all the tiny little details that were included in the game.
Subsequent games don't seem to have the care that was taken, or the showing of love for the game. Indeed, especially with 4, the impression is given that at least one of the developers doesn't really care about the game, and indeed seems to appear contemptuous toward it.
The studio also seems to be so out of touch with what players want and seem much more concerned with shoehorning "social issues" and political correctness into the game than much else.
Edit - Also in regard to this "TS4 is the best selling Sims game of all time" , that I wonder if they count the times the game has been given away for free. Which is certainly quite a bit. To me, that does not count as making it the best "selling" game of the series, when it has been handed out like halloween candy.
I am not sure TS3 has ever been given away for free, and they stopped giving away the TS2 UC, more than likely because it is much better than TS4
