The best way to explore the ancient temples and sites is to see Bagan by bike.
Despite what guide books say it is entirely possible to see Bagan and surrounding in a day or two unless you really want to challenge yourself and tally every time you see to cross off the 4000+ temples that dot the landscape.
I rented a simple pedal bike with no gears for just $1US and managed to reach all the top spots in a day. After seeing 20 temples or so they become repetitive in many ways. On my second day, I rented an electric bike for just $3US for the day which gave me the energy to climb the many steps each temple you may come across.
Unlike Angkor where each temple is distinctly different and a jungle setting to match, Bagan is dry and more bush-like. It doesn’t make it not worth the visit but personally, the temples of the Cambodian Angkor are far more impressive.
That said, they are two very different cultures in history.