The name of these things is something I dismissed as an inaccuracy for a long time. I was thinking of spoilers in terms of plot spoilers, which these guides have virtually none. All they tell you is how to complete the levels and where all the secrets are (and the latter is even incomplete in some entries!). This dismissal of the guides containing spoilers was before I really contemplated the sting I felt of asking someone where the 7th dungeon in Zelda is and he pops up a game map with a red circle on it and says "use the lantern on that bush," or when a friend and I caved in to going to gamefaqs after spending 2 hours on the last puzzle in goof troop.
Notice that these games stories aren't deep (sorry, zelda fans, but a complex timeline doesn't make the first game more than what it is). So, in gaming, a 'spoiler' doesn't have to be a plot spoiler; it's usually a solution given to problems presented in the game, which takes away from the satisfaction of solving that puzzle or finding that secret yourself.
But Marathon is different. A lot of the game's plot and lore are hidden in secret terminals. Let's be honest here: did anybody find the Gherit White terminal without spoilers? I sure as hell didn't grenade hop onto a narrow platform to open an out-of-sight-door that closes far too quickly to read about the s'pht resurrecting Tycho with a Durandal-copy to make him rampant without any prompting from a guide. That wasn't the spoiler for me. I was combing those maps for 100% completion and didn't hesitate at all to look it up; however, what I wouldn't read was the text of those terminals before getting to them. Because that was the real spoiler (and maybe 'cuz it's too hard to link up the terminal archives with which ones they are in the map).
The most spoilerific it can get in the aspect of game progression is crap like Colony Ship and Thing What Kicks, which are BS switch 'puzzles' that are unintuitive and I can't blame anyone for throwing up their hands in defeat (I do remember toughing it out all day in thing what kicks swimming around for something I missed until I got it. What a load of f'lick'ta sewage that button is).
So, what do you think? Are the spoiler guides spoilery?