Adventure Generator Vol. 1 includes four d20 tables, but it goes beyond the madlibs-style of adventure creation or the hook approach.
The tables are: adventure type, environment, adversary, and theme.
The adventure type table (and the accompanying text) is the heart and the main value of the generator. You get ten adventure types. Volume 2 provides ten more. If you like what the adventure types offer (which I'll describe below), you'll probably like the Adventure Generator (either or both volumes). If it doesn't sound like your style at all, this isn't the product for you.
The product description says the Adventure Generator is for a fantasy setting, but the adventure types themselves aren't specific to fantasy. You could use these same adventure types in a variety of genres with little or no tweaking.
Each adventure type gets about 2000-3000 words of text. First, it gives you an adventure summary. The "Block by Block" adventure has this summary, for instance: "The player characters head into a dangerous situation to rescue someone from the adversary and return them to safety." It goes on to offers tips for basing an adventure on that summary: Adapting for the System, Adapting for the Campaign, Adapting for the Environment, and Adapting for the Adversary (one or a few paragraphs each).
Next, each adventure type lays out a five-encounter model, which is reminiscent of (but not identical to) the Five Room Dungeon model by Johnn Four. Whereas a Five Room Dungeon leans toward adventures that are relatively quick and lean, Adventure Generator gives a deeper treatment. It describes the storytelling function of each encounter as it relates to the particular adventure type. For example, Encounter 1 gives tips on establishing the situation, demonstrating the stakes, and creating character connections. In other words, you're getting "here's how encounter N fits into the adventure" instead of "here's who you encounter" or "here's what the PCs must do."
You get tips on where and how you might expand the number of encounters or tweak the model, such as: "If you wish to expand the adventure beyond 5 encounters, this can be broken into a separate challenge."
Some people automatically declare "railroading" the moment they see anything resembling a structure, but the Adventure Generator isn't railroading. The encounter descriptions don't dictate to the players how they should achieve the aventure goal. The descriptions don't limit player choices. They also don't limit the GM's options. Knowing that Encounter 4 is a good time for "adversary retaliation" helps you (as the GM) adapt to the situation. Maybe you have some ideas in advance. Maybe you improvise on the spot, based on what's happened so far and any previous ideas you had. "Adversary retaliation" is inspiration and guidance, not a script that must be followed.
The environment types and adversary types are all things you've seen before, if you're familiar with the usual fantasy RPG settings. You get a brief paragraph on each environment that probably won't tell you anything new. For the adversaries, you get one of the usual fantasy adversary types (humanoids, undead, etc.), with a brief paragraph on what they are and a list of example creatures of that type. You might find them helpful, but most likely, you already have your own ways to choose adventure settings and adversaries, and they're already adapted for your setting. If you have those resources, you might not be interested these two tables. If you don't have such resources, environment and adversary tables here give you broad types, not specifics, so you'd still need to come up with the details you need.
If you have your own environment and adversary resources, you're also not confined to the fantasy genre. You can use the adventure types and the themes in other genres, using your own methods for devising the environment and adversaries.
The theme table, marked optional, gives you "something akin to literary theme" for focusing the adventure conflicts in a particular direction. You get ten themes, such as "Crime Doesn't Pay" or "Humanity vs. Society." Each one gives you a couple of paragraphs discussing the sorts of conflicts you'd see with that theme. The theme is basically a lens as you develop the adventure. If you decide that your theme is "crime doesn't pay," then you develop the adventure with a focus on wrongdoers trying to get away with wrongdoing or eventually getting what they deserve.