I heard Act One and it's a revelation (3-6)
I believe the answer is:
eye-opener
'it's a revelation' is the definition.
(I have seen 'unexpected revelation' mean 'eye opener' so perhaps 'revelation' could also mean 'eye opener')
'i heard act one' is the wordplay.
'i' becomes 'eye' (I've seen this in other clues).
'heard act one' becomes 'opener' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'eye'+'opener'='EYE-OPENER'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for eye-opener that I've seen before include "Surprise revelation" , "Surprising fact or circumstance of ocular origin" , "Something startling" , "Startling revelation" , "Revelation or enlightenment - with optical reaction?" .)