It all depends on where I am, and who I'm with.
My usual hangout works hard to be an immersive RP style sim, and people there do a good job. It's a team effort, really - everyone kinda shares the same goal. We might not all be trying to live another life, or be another person, but in some ways we're all looking for a little escape from the everyday.
SL gives you all the tools you need to do that. It just comes down to finding the right people to do it with.