So …! (surprise): adjective + vậy / thế

Right after an adjective, vậy means "so", with surprise: Đông vậy! It's so crowded! It says "this much? I didn't expect that." In Hà Nội it's thế: Đông thế!

Very often it's a question with sao (why) in front: Sao mắc vậy chị? Why is it so expensive? (in Hà Nội, Sao đắt thế chị?). Sao hôm nay em về sớm vậy? Why are you home so early today? Here vậy both says "so" and softens the question, as it does after đâu or gì.

Compared with quá, which reacts to how good or bad something is, vậy reacts to how much it is compared with what you expected. Nóng quá! is "It's so hot!"; Nóng vậy! is closer to "Wow, it's this hot?" Both are everyday speech, and quá is the more common exclamation.

Như vậy (like that) is the fuller form and means the same here: Sao đông như vậy?