HHR is definitely a car worth your attention. It runs very smoothly and quietly, gives you great gas mileage (30 miles highway plus local in my case) and plenty cargo space. My HHR has a 2.4-liter engine for which premium gas is recommended (you can still use other grades but later on your engine may need to be serviced). I've noticed that whenever I'm driving up-hill, I really need to push the paddle to maintain the same speed. The only thing I don't like at all about this vehicle is the little compartment space. My previous car is a Geo Prizm (much like Toyota's Corolla) which is quite smaller than HHR. But Prizm has more space where I can put CD's, maps, stuff like that.
Excellent retro-looking exterior design (biggest reason why I bought one); very quiet and comfortable and fun to ride; plenty of cargo space.
Definitely much more compartment space inside the car for people to put stuff like CD's, maps, etc. Also, like many owners have pointed out, the location of front-seat cup holders as well as power window controls can be improved.