A portion of a review from PopMatters:

Grant Rodiek said in a Gamespot interview that Maxis added the Stylist and Architect career tracks because “Many Sims players never leave build mode or create-a-sim, and we wanted to combine the gameplay found in these creative toolsets with the storytelling and simulation aspects of the rest of the game.” Players who obsess over creating the perfect house or a stylish wardrobe for their sims can now achieve rewards in game for doing so, and the process also creates a narrative and is connected to the stories of the NPC sims as well.

Another major change to the gameplay is related to the new Firefighter and Medical careers: natural disasters. I haven’t yet witnessed an earthquake in game, but from what I understand, natural disasters can occur, and when they do, they start fires and cause injuries. You’d better hope that you’ve got a few trained professionals on hand to deal with the fallout when it happens. Like stylists and architects, firefighters and doctors have flexible work hours and get paid upon completion of a task. They can also build skills and pursue relationships while on the clock, if they can find time between emergencies.

One of the coolest innovations that nobody seems to be talking much about is the self-employment option. Many a sim has adopted a work-at-home career like painting, writing, or gardening to support small children while saving on childcare costs or to supplement income from a low paying career. Now these sims can register as self-employed at City Hall and track their career progress just like any other sim. They don’t get weekly stipends or paychecks, but they do get bonuses to the value of their goods in direct proportion to the number sold.

review here