Player agency is a critical element of role playing games to me. One of the things that great dissatisfies me about most series of modules is how much they tend to need the story to progress in a certain direction. The label ‘Adventure Path’ itself rings player agency warning bells in my head — ‘path’ implies a linear relationship between the adventures.
The GDQ (Giants-Drow-Queen of Demonweb Pits) series of modules is often held up as an example of how a series of modules can be done well… but I have to admit that as much as they could be a wonderful example of sandbox adventures, they honestly don’t work for me that way. Individually they mostly aren’t bad, in that they presented as a situation, a problem to be solved. The approach to each one has some options, so there is some player agency involved in the situation… but from my perspective, there is little player agency about getting involved. The entire series is driven by “go here or else” and really no way to not find the next module.