Let me count the ways
1. Gas economy. Doing my part to break from foreign oil. And saving my wallet at the same time.
Last tank: 52 mpg. Current tank 54.6 mpg
2. Low emissions. While 10% isn't what I primarily bought it for I am just gloating that my car produces 90% fewer emissions than anything else on the road.
3. Solid quality. I love shutting the driver's door and hearing that solid "chunk" sound. Compared to my Saturn, the Prius makes my Saturn a bucket of bolts. The Prius transmission is smoother, the pick up is better, the ride is smoother. Even the seats are better and my Saturn had leather.
4. Hatchback. I love having a hatchback again. My first two cars were hatchbacks, although the Nissan was designed stupid. The trunk of the Saturn never held that much even with the seats folded down. Now I've got four doors and can use the back seat, or I can use the cargo area or I can use both. The Cheesy plastic I can live with. I've already bought leather covers for the glove box, driver's dash and all of the armrests and console cover. I can certainly live with the interior for all of the other benefits this car has.
My next car will be a Prius. It will have a gray interior next time around. And depending on improvements I may not wait 10 years, which is my normal car buying cycle. I may buy early. Just as long as it's still a hatchback I'll be happy.