I've been a big fan of the Sims games for a while, and I think this is easily the best one yet. Visually, the game is gorgeous, and has a vibrant and clean style. I don't have a very powerful computer, and the game still runs beautifully with the graphics turned up. The building functions are great, and have been smoothed over and simplified compared to Sims 3. There is unfortunately no terrain editing, so you can't be as creative when building. There are also limited customization options for furniture and decorations, so things feel a little more basic and constrained at times.
Gameplay is great, and I love the new ways Sims interact with each other and the world around them. They can multitask pretty efficiently, and don't take as long to do simple tasks as they did in previous games. The animations during things like working out, talking, etc are much more natural too.
CAS is fantastic, the Sims look awesome. The clothing and hair is much more realistic and interesting than before, and they seem more unique. The tattoos are much more versatile and stylish than they were in 3 as well.
Overall, a fantastic addition to the Sims franchise, that I can't stop playing.