Enough to keep the viewer completely occupied (6)
I believe the answer is:
eyeful
'enough to keep' is the definition.
I can't judge whether this defines the answer.
'viewer completely occupied' is the wordplay.
'viewer' becomes 'eye' (organ which sees or views).
'completely occupied' becomes 'ful' (I can't explain this - if you can you should believe this answer much more).
'eye'+'ful'='EYEFUL'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for eyeful that I've seen before include "Good long look" , "beauty!" , "Interesting sight - beautiful woman" , "One who is well worth looking at" , "A (lovely) sight to behold" .)