I've had a go in two sims including BA's 777 and really enjoyed them. The instructors/pilots can adapt the sessions for any skill level.
I think the best format is a longer session with a few friends so you both get to observe and fly.
There's also a big difference in the graphical capabilities of the different models of sims - the older ones don't have good visuals because it's not that important for their main purpose and that can be a bit of a surprise if you are used to PS3.