4 or 5 years ago I went to Erawan Museum, took a look at the facility from the entrance, and decided not to proceed any further. It looked a bit sketchy. However, yesterday I decided to try again. It appears they have invested some time and effort into cleaning the place up so I proceeded to enter.
Many reviews complain about the entrance fee but it is only about $12; not much compared to what you spent on your airfare to arrive in Thailand. The interior of the museum is pretty unbelievable -- the details of the artwork, the colors, the meaning of the architect, etc. It is definitely a feast for your eyes! And you can't help but wonder how they were able to build such a beautiful facility.
There is also a beautiful garden surrounding the museum where it is nice to spend a little time; quiet, shady, lawn furniture available for your use, various statues, etc.
The museum is quite easy to reach. Take the BTS train to Pu Chao station (E16), look east (the direction your train is now heading) after exiting and you will see the elephant statue. Very easy 10 minute walk from the station.
So glad I finally visited the museum. My only suggestion is that you remember this is a public place; not your private photo shot studio. The museum has a beautiful open staircase that splits into 2 stairways leading up on both sides of the building. While visiting, a couple of ladies were using both staircases as their personal space to take photos with no consideration that other people might want to also use the stairs. This is a temple. Be respectful of your surroundings, dress appropriately, and be considerate of other people around you. We all want to capture some great photos to take home with us.