Here's a thought I have, I wonder if others feel the same.
Out of the four games, I preferred ToN the most, by a long way.
Now a lot of that is because I preferred the map, the girls and the story, but there is another feature that, for me, is absent from TGO and SotS.
When I discovered ToN, it was already complete, I bought the game and I could play it exactly how I wanted. If I just wanted a quick 10 minutes I could, if I wanted to spend an hour I could.
Also because the game was complete it was more of a challenge. With updates, I get a short packaged piece of gameplay and I'm told exactly how many things there are to do and find. I know if I find a chest there will be a chest key somewhere in the update. And because the updates are slithers of gameplay it is easy to watch a guide and work out exactly what you are missing.
But when you play the full game it is all open to you (albeit some areas don't get opened until you progress). When you find a chest key it can fit any of the chests so you may not open them in the same order that you do when you play updates. Indeed you might have two keys and five chests.
Ideally, I would have waited for TGO and SotS to complete before buying and playing - trouble is I'm addicted and can't resist the updates - wish I could, but I have no self-control.