TS1 was ground breaking and really dark and fun but I only felt in love with the franchise when TS2 came along.
TS2 felt like it was made with love. It had its flaws of course (like time!) but overall, I played it with a joy I don't have anymore.
It was quirky and had an immense amount of attention to detail. It was a massive change from its predecessor, it felt like the greatest upgrade a game could get. Life stages were revolutionary for me. The memory system, the fears and wants, the attraction system, the NPCs, etc
It had depth and was like the nicest homemade comfort food you can think of.
Then TS3 came and added open world, a huge step forward in the franchise, but lost its heart for me. I still played it like crazy but it felt more shallow and had a lot of bugs. To keep my analogy with food, TS3 was comfort food yes, but from a chain restaurant.
Lastly, we got TS4. It added a more intuitive Build mode (but full of restrictions) and a more fleshed out CAS (but no colour wheel). It didn't feel like it upgraded and improved anything massively like 2 and 3 did. I like it, but it's very shallow and has no charm. It also feels extremely limited in many ways. It is also comfort food to me, but from the supermarket, a ready meal that you heat up in the oven.
Oh boy! Now I am hungry! :D
