Angkor Wat temples are scattered over a vast area. It reminds me of Bagan in Burma where I saw thousands of pagodas.
A 1-day, 3-day, 1-week pass costs US$20, 40 and 60 respectively.
I bought the 1-day pass. For me it was enough. With my bicycle my range was extended but to cover the whole area would have taken me days.
(BTW, have you booked your ticket to Siem Reap? Seems air tickets from Singapore at least are selling out very fast.)