The first (and last) time I went to Bangkok was when I was kid travelling there with family. My question is how much has the city changed in the past 15 years (or more)? Anything I should know about getting around?
A serious amount has changed! Traffic is a lot better (but still pretty dire at rush hour). There's a metro and skytrain which makes getting around a lot easier but there are still plenty of tuc tuc's! In general transport is so much easier than it used to be so you'll have no problem getting around.
If you're a fan of (touristy) night markets, there are definitely more than there used to be and I feel like you do get hassled a bit more, but it's not that bad!
I think the Skytrain was built just about 15 years ago so if you haven't seen it it's going to be a big surprise. It can get you to so many places -- the Jim Thompson House, the Siam Center, etc. It's incredibly convenient and easy to use!
Mentioned in this answer:
In 15 years many change now two airports, subway, and bts it s a subway outside. Many new building and roof bar.
For the classical visit temple etc still the same place. Traffic jam same but more shopping mall and the price grow up.