For me the selling point on my starting my Sims journey with TS3 was the open world (which caters to my style of play), I love exploring my world and having to be confined to one spot; not seeing story progression with other Sims, just didn't appeal to me. That's why I also intend to download CAW one of these days. Also I use CASt extensively as well. I also spend a lot of time (I'd say 60/40 split between building/gameplay) building houses. And I will rebuild a house from foundation to roof if I find that my routing has gone haywire. I've torn down a completed house because my Sim took fifteen sim minutes to get out of the house in the morning. I'd even go so far as to say I'm obsessive when it comes to building efficient houses that let my sims get out of the house in the morning to go to their rabbit-hole jobs as quickly as possible.
I also use terrain tools extensively. I grew up on a country lot on the side of a hill...so I can't seem to get away from enjoying some terrain differentiation in my lot. My view is that flat lots are for city neighborhoods. I also use ponds excessively too...but I guess I could learn to live without for a while...if I knew they would come back in an expansion or an update.