The variety of shapes and sizes of the temples, from small stupa to huge reclining Buddha, and the sheer number of them, make Bagan one of the most incredible places to visit in Asia. Do not short change it with a one day visit since one can easily spend 3 full days and not see and do everything worthwhile. Highly recommend getting out into the temples very early to watch the sunrise from the top of one of the taller ones (don't worry -- you will have company as this is a fairly popular thing to do!). You can see a lot on foot, but the horse-drawn carriages are a very enjoyable way to get around.
If you own or manage Bagan Temples, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.