Disappointment may arise from driving a hybrid the way everyone drives regular cars, revelling in the acceleration that is boosted by the hybrid system over and above the standard version, and braking to a stop just before hitting the last car at a light. Car dealerships with the exception of the Prius sell the customers with those tales of how much better hybrid versions accelerate, and when you consider the inertia involved, means the same old huge gas consumption.
You have to change the way you drive and drive for a substantial period of time every time you drive, or you will be disappointed.

2007 Prius, 4.0 liters per hundred K