You aren't really thinking, you are reacting here. You are trapped in a maze. Your freedom to make decisions and alter the course of the adventure is blocked off by cold stone walls. You are expected to be the rat in the maze, wander around, and fight against oppressive limitations to show some individuality. There is the illusion of choice, but there really isn't much choice except for, "where do we go next?" Watch this:
Contrast this with non-linear play. You are a cowboy walking into an Old West town. Go from there. Do you rob the stagecoach? Do you wander into the saloon and look for trouble? Do you respond to that "help wanted" poster on the sheriff's office? Do you stand up for that lanky prospector being ruffled up by the local ruffians? Do you watch as the two gunfighters stare each other down?
You are only limited by the hooks and opportunities the referee presents to you. You area free agent, and you are free to chase down whatever hare-brained idea or silly course of action you can imagine. Like an open-world sandbox game, whatever you do is fine. A great referee will improvise and wing it for the whole session, and react to whatever the players come up with on the fly.
Dungeons are easy, and they focus the group's attention on one situation and location. They are useful and create tension, but after a while, they begin to feel artificial and limiting. There are no other options but "door A" and "hall B." Our group has done them to the point where dungeon based modules elicit groans from my players.
So in our Savage Worlds: Pathfinder game, we are banning dungeons. No more holes in the ground, we are tired of them. There still can be lost tombs, ancient ruins, or similar pulp-inspired sites of mystery and wonder - but not to the extent where being a mouse wandering the maze is the point of the game. If it has more than a handful of rooms or passages, forget it, we are not interested. It isn't like historically, here on Earth, there have been great examples of massive underground dungeon complexes.
Still, a pulp-inspired underground massive ritual chamber is fine. A giant maze where you have to map and wander around aimlessly is not. A lost tomb with a central corridor and adjoining chambers (for mummies to break out of) is fine, a tomb that takes up an entire piece of graph paper where the entire session is spent lost in the corridors is not. Pulp-adventure means classic action-movie inspired sets and locations, real Temple of Doom stuff, and fun and dynamic locations.
Like the stuff you see in the books, and exactly like the above. I admit, the Paizo team does a good job trying to make their adventures and world exciting, action-inspired, and fun looking - but I get this sense the d20 tactical dungeon rules fight them. The rules drag the world down. What looks fun on the cover in reality, at least when we play, is a mess of stat-blocks, slow-playing rules, tracking conditions, slow combat, and slogging through a rules system that should be "fast, fun and easy to play" but isn't. Especially now with all the books and additions to the core system.
I want the game to play like the pictures. I do not care about supporting rules which get in the way of fun. A fighter is a someone who knows how to use a sword. A mage knows magic. A thief is sneaky. Powers are powers. People learn the things they choose to learn. The people in the artwork do not have leg shackles on them chained to large iron d20s. They are "adventurers" in any game system. That mage above? Just casting a spell, and in my game, something from the Savage Worlds rules. And something not converted over, and no-one in this world speaks of levels, alignment, classes, or magic missile.
It seems dictatorial, but conversions like this are notoriously weak-legged, with that feeling of "lets go back" to the original rules hanging over the game. Being clear on "what this game is going to be like" helps a referee keep it on track, helps players know what they are getting into and how to act, and it sets expectations on how much of the original source material from the rules is going to be used. You don't want to be playing, have a player expecting to play a specific "mesmerist" or some other in-the-game class, and have that player expecting one thing while the game is doing another.
In this case, none of it. The Inner Sea World Guide is the game's bible for "what the world is" and "who lives there." That cover sets the tone for the game. The pictures of adventures and battles inside also set the tone. The peoples and places inside exist in this world.
And then the Savage Worlds rulebook is thrown down, right on top. These are the rules. This is how this world works. You should be good from here. This is how the game works, how it will be run, and other Pathfinder rules-focused books will be ignored.
End. Stop. No new books needed. Except maybe...
...and here is where the tricky part comes in. I am going to put up a yellow light when the question of "monsters" comes up. You may want to go with the standard monster list. It's easy. You may want to crack open the bestiary book to pull in some foes, and then find yourself converting monsters over. And then the slow drag of "it would be easier to go back" starts to be felt.
My advice? Don't do it. It's a trap! Stick with the monsters with in the Fantasy Companion. "Re-skin" them, if needed to look and act like the monsters you need. Remember, you are going for "pulp-adventure" not a "d20 simulator." You absolutely do not need a complete monster list to run this game; some orcs, skeletons, zombies, and a big boss beast is fine and will get your adventure through many nights. Most players probably won't notice your monster list isn't the "complete Pathfinder approved" monster list. As long as you have one or two of the recognizable "fantasy monster types" you are fine.
You are fine.
And here is where you can have some fun. You can invent new monsters now. If you reject the "standard" list, you can invent cool new monsters like a fire-elemental mummy that vomits lava and is immune to fire magic, and all of a sudden - no one knows what to expect next. Your game goes from the familiar classic-rock playlist of the d20 "greatest hits" monsters to something cool, all yours, and unique. You can mix in the old standards once and a while, mod them, or make new monsters based on your imagination.
It's like that monster on the cover of the Bestiary, the "giant troll" thing in the background. I don't care to go and look that up in the Bestiary, I will say that is a giant troll and I will go and find some stat-block for a giant in the Fantasy Companion and give it regeneration and a weakness to fire, and blammo, you are done. A giant that regenerates? Color me terrified as a player in this game and trying to deal with a beast like this. If you were a slave to the "official monster list" your mind will not be thinking like this, and you will lose all of your creativity and imagination.
Do that. Look at the pictures in the books, and come up with your own creations. That flaming dog in that picture is an "inferno hound" and then go wild giving it powers and weaknesses based on what it looks like. Your imagination and silly creations will make this game special. Refusing to be a slave to the "official lists and rules" will be your freedom. Don't go too wild, a normal griffon is still a griffon fro mthe book, but for the special and memorable monsters, have fun.
Same with magic. Same with powers. Same with magic items. Same with heroes. Same with everything. You are free to be inspired by the pictures, not ruled by the words.
Your players are not grading you on how well your conversion looks like the source material. They will not judge you that a "giant troll" doesn't exist in the Bestiary and "you obviously made something up." Gasp! The horror of doing something not by the official rules! Your game is invalid! You obviously aren't as creative as the books you paid for. You will never be able to play in a store or convention game again. Really? Sarcasm over, but honestly, these feelings come up when you dare to be creative and do your own thing. It's a byproduct of companies wanting to sell you more books, and that is their right, but never let the fear of an "official seal of approval" stop you from doing anything.
It's your game. Players are here to have fun. They will judge you if your game was interesting, fast paced, fun, and it provided a great night of entertainment.
The more input you have in your world, the better it will be. But the number one thing getting in your way of having fun is yourself and your slavish loyalty to a stack of books. You need to break those chains for this to be fun. So go ahead and break them.