For me, The Sims 2 always feels more open-ended, because of the possibility to lock wants/fears and fulfill/realize those wants/fears. If you consistently realize those fears, then you can send your Sim to the Therapist pretty often, creating the illusion that your Sim has to combat aspiration failure / mental illness for a very long time. This is great for a sadistic type of player who likes to watch Sims go through life and watch them fail at their tasks.
The Sims 3 allows Sims to have fears, but those fears cannot be realized anymore. Instead, Sims may get negative moodlets, telling the player if he/she is afraid of something (i.e. the dark). Coward Sims are afraid of the dark and probably other things. The Sims 3 playstyle is more focused on fulfilling those promised wishes and earning LifeTime Happiness Points/Rewards.
I can see why a The Sims 2 player may not like The Sims 3. TS3 may feel less open-ended, because everything is all positive and towards some kind of goal. You get wishes, promise those wishes, earn LifeTime Happiness Points and buy Rewards with those points. Torturing Sims is harder, because Sims are smarter and can get out of the pool without a ladder, so Skip Broke in TS3 will probably not have that "pool ladder accident". There is no aspiration failure, so no need of a Therapist. And, Insane Sims will just be Sims with the Insane trait. With that said, I can also see why TS3 fans may not like TS2, because TS2's goals are too easy to fulfill. In The Sims 3, the LifeTime Wish and LifeTime Rewards are rather challenging and time-consuming, and the rewards are plentiful. Meanwhile in the Sims 2, the highest aspiration reward is the Elixir of Life, and even that can fail depending on the Sim's aspiration level upon use.
What kind of Simmer are you?