Repeated blissful experiences in meditation
From the theravada perspective, you ought to master each jhana. That is, you should have reasonable control of it, enter when you make a resolution to enter, keep it stable and leave when you make a resolution to leave. So you should be able to replicate it. If you identify important factors that are weak, these are factors that need further development. Weak jhana factors mean one does not fully understand their conditions, what obstructs them, how to cultivate them, control and keep them stable.

This is roughly the full jhana/samadhi meditation curriculum, though it can be argued that full mastering of jhanas are optional when pursuing the goal, in favor of mindfulness/sati meditation.

I believe Pa Auk Sayadaw considers a student to have mastered a jhana if he or she is able to enter at will and stay for 3 hours in it (period that testify the meditator skills in stabilizing jhana). This is also what he recommends before moving to the next jhana, which can be impossible to access without a minimum control of the previous jhana (e.g. as the factors to be abandoned might be too strong and unfamiliar to be properly controlled)