The 'shudder' that some reviews mention is most obvious at low speeds, and you would never feel it at highway speeds (because the ICE is never OFF at highway speeds). At speeds between 15 and 40mph, the transition is smooth enough that you might not notice. I did not notice any difference between the Altima and Camry hybrids in this respect, when I was shopping this summer.

The thing that I had to get used to was the variability in the throttle response (i.e. how "heavy" or "light" the accelerator felt), depending on how much the electric motor was boosting the ICE. Not in a bad way, just not what I'm used to (having driven manual transmissions my whole life).

But do test drive it for yourself. There's no substitute for first-hand experience.