I'm certain many people will agree with you about building. It can be pretty fun, especially with all the building contests on this site (I'm often devoid of my own ideas for themes, so thank you!).
I spend hours fiddling around in CAS. From recoloring clothes to working on that Kurt Cobain sim that looks finished, but I doubt really is. It's therapeutic for me, and the sheer amount of sims saved to my bin reflects that.
For gameplay, I really like the firefighter profession. I think it stems from my first decadynasty attempt, where I let Blaise Kindle live out her dreams of fighting fires. Between the close connections you can have with your co-workers and the thrill of finally saving some sims, it's just a really fun thing to do. When I finally restart my immortal dynasty, one of the generations is going to be a firefighter, no matter how hard it is.