I have a 2002 Trailblazer and I agree the gas mileage sucks but mainly if you are hard on the gas. My wife is the main driver and she's getting about ~20MPG. Reliability?? Probably average for a domestic vehicle I'd say... The upside is the price..
You can find some amazing deals on lease returns.
We love that truck, we had a Ford Explorer which was Ok but the trailblazer is just amazing. We're very happy with our truck.