Rule Number One

White Box: Fantastic Medieval Adventure Game
When a game booklet titles itself White Box, I generally take a look. The White Box Fantastic Medieval Adventure Game by Charlie Mason and Seattle Hill Games is a re-imagining of not only the Original White Box, but also Swords & Wizardry's White Box. Right away Mr. Mason catches my attention with his interpretation of RULE ONE

The most important rule in White Box is that the Referee always has the
right to modify the rules. In fact, it’s encouraged! This is your game, after
all. There are gaps in the rules—holes left open on purpose—because much
of the fun of “old school” gaming is being able to make up rules as needed.

...because much of the fun of "old school gaming is being able to make up rules as needed." Exactly! It can be a challenge to make up fair rules that add to everyone's enjoyment of the game, rules that encourage creativity, rules that don't limit options, but that reward thinking outside the box, rules that will be just as applicable later in similar circumstances and can become part of the body of house rules or "how we play the game". But all that is part of the fun of being referee especially and to some extent even being a player of the "old school game" as I see it.
If looking in a big book for the rule that comes closest to covering the situation at the table has more appeal, there are other games available. Arguably no rules can cover every possible situation, but some probably come very close. Having an official rule is very satisfying to many RPG fans, and I don't intend to belittle that style of play. I regularly play those games myself (although I don't like to pause the action to look up rules). Sometimes I like to make stuff up on the fly. It's fun to come up with a good ruling that seems to satisfy everyone and keeps the action at the table rolling.
So besides a great Rule One, what has White Box Fantastic Medieval Adventure Game got going for itself? Well, it's a very nice looking book, nice art, attractive layout. The book can be ordered online with one of three covers and in softcover or hardcover.

There's more than just a nice package however. I favor multiple saving throw categories like in the Original White Box. Swords & Wizardry White Box drops the multiple saving throw system for a single, universal saving throw. White Box Fantastic Medieval Adventure Game is based on Swords & Wizardry, but gives an optional saving throw system based on class and level and situation. So when the dragon breaths (Dragon Breath) the saving through is different than when the basilisk gazes your way (Paralyze/Turn to Stone). There are fans of the single saving throw value, but I like making those choices as referee between asking for a saving throw verses Dragon Breath or Paralyze/Stone when a rock-slide threatens the party. Is it more a quickness thing or a resist fear thing? In a way it is similar to the fun of making up rules deciding which saving throw to call for.
White Box Fantastic Medieval Adventure Game is well written and entertaining to read. It takes a definite stand on many of the ambiguous points of Original White Box, such as alignment - White Box Fantastic uses the three classic alignments, but equates Law with good and Chaos with evil. Of course a referee who disagrees with this rule, like any other, can play it differently. Options abound with most White Box style games and there are a number of "optional rules" that are presented here. Classes are the basic three with the addition of the optional Thief. If used, the Thief has a special ability called "Thievery" giving one the ability to roll a d6 to pick a pocket, open a lock and do other thiefy things. The score needed on the d6 gets easier to make as the thief goes up in levels.
Races are the usual Tolkienesque Human (default), Dwarf, Elf  and Halfling. The non-humans are restricted in class choice and level maximum. Elves are the go back and forth between fighter and magic user or an optional B/X style combination. None see in the dark!
Weapons follow the general White Box trend of all doing a d6 damage, except some have a -1 or +1 added. Again, White Box Fantastic gives the referee the stated option to use the old everything does 1d6 damage system. Armor class can be done ascending or descending, according to preference. There are alternatives to several factors of combat making it one of the most easily customizable sections of the rules. If diplomacy and negotiating is more to the party's liking, there is advice on handling that. As a nod to the old school, jousting rules are touched on. (Having read some old King Arthur tales recently, I am inclined to include more jousting as a part of play.) There is also some decent referee advice on running the game, keeping track of time and handling the outdoor and dungeon environment. Discussion continues regarding adventure and campaign creation and awarding experience. Here White Box Fantastic Medieval Adventure Game takes the traditional experience for gold approach, but provides some justification for this system and offers some options. Rather extensive bestiary and treasure sections complete the book. This is White Box, so magic swords have intelligence and their own ideas of what should be done (always fun for role-play as the fighter has an argument with the sword).
So the hobby has another White Box. White Box Fantastic Medieval Adventure Game is a sound addition to the stable of White Box imitators, simulacrum, clones, pseudo-clones and re-interpretations of the Original Fantasy Role-Playing Game. Most I have read are useful in that they offer a more complete statement of the basic principles of role-playing, dice and general game play than the Original which is good for beginners. In other words, there are some "training wheels" included. The Original White Box allows for more interpretations than is usual among the later "White Box" rules. Rather than encouraging the referee to make decisions about the rules, the Original insists on it. Why? Because making up rules is fun! That's Rule One.