We all need to remember how boring the Sims 2 would be with no Expansion Packs! They all start slow...the EPs will come probably every 6-12 months.
They are both fun games. But the sims 2 is more my style of gameplay. I play multi generations and multiple families. I like seeing where my sims go and what they are doing.
The sims 3 has a lot of great features. I have fun with it. But as others have said, I don't see what is wrong with playing both. Just because something is shiny and new doesn't mean we have to abandon our old games.
I plan on rotating the sims 2 and the sims 3. Like 2 days of the sims 2 and then play 2 days of the sims 3 and keep doing that.