I actually played that old Sims MMO back years and years ago. Sims Online I believe.
For a Sims 1 based online game it was really good. lol
I really think if they made a jazzed-up version of the Sims MMO now, it would be ridiculously popular.
I don't know a ton about Second Life, but it's always seemed like the Sims MMO would be what Second Life wishes it was. Except in the Sims you wouldn't be able to fly ... I've heard flying is a part of SL.