Obviously you were impressed by Angkor watt . Many of the temples/wats of Cambodia are of interest. However, in Vietnam if you study the architecture of the country you are studying its history. Very roughly, you can start with the Ly dynasty (11th-12th centuries) then Tran (13th),to Le (16 & 17th), finally the Nguyen dynasty of the 17th to mid 19th century. If you like French Colonial you can continue forward in time and design.
Each period has its own unique design and I will list ref at the end as the architecture of Vietnam is so varied and distinctive that it deserves your study.
Thailand’s architecture is varied although not as much as Vietnam’s. If Angkor Wat impressed you, you should like Pradat Hin Phimal, an example of Khmer architecture found in Thailand. You might also find Wat Rong Khun, a 20th century temple, still under construction
Ref: Vietnamese Architecture by Le Huu Phuong, Dec.22,2016. Traditional Vietnamese Architecture by Nguyen Ba Dang, Nguyen Vu Phuong & Ta Hoang Van, Gioi Press, 2013.