这句子是由as.as 引导的比较状语从句,第一个as是副词修饰 good,第二个as是连词,像...一样,句子意思是这家旅馆不像他们预料的那么好,这是个省略句,补全应该是
the hotel was not as good as they expected( it was good).是把和前面句子相同的成分省略了,所以这里就不能用what了.
如果说成是what what they expected 就是他们期待的东西.
eg .They got what they expected ..
what they expected 在这个句子中是宾语从句