If you are familiar with BRP you can skip the next four paragraphs as it covers the basic history and basic system description.
The Basic Roleplaying system (BRP) has been around for quite a while (RuneQuest 1978) and is one of the most well known roleplaying systems still in print today. Unlike many RPGs, BRP has stayed true to its core mechanics over the years. Sure each new game that used the system had its tweaks and add-ons but the core percentile system stayed pretty much the same throughout. Several games that were popular during their times have used the BRP system including RuneQuest, Worlds of Wonder Boxed Set(Super World ,Future World & Magic World), ElfQuest , Stormbringer, Ringworld, Hawkmoon and multiple European RPGs. In recent years BRP has been most notable for its use in the Call of Cthulhu 6th edition.
My experience with BRP is almost solely with Call of Cthulhu where most of the subsystems included in this book are not used. That said, from what I've read on BRP it includes nearly all of the optional rules from all of the Chaosium versions of the BRP system.
For those that have not played BRP it is a percentile skilled based system: to succeed at a task you simply roll under your skill percentage. The characters characteristics (STR,CON,SIZ,INT,POW,DEX,APP, and EDU) , somewhat strangely, are not expressed in a percentage but instead are based on a 3d6 roll and give a range of 3-18. These characteristics in turn are converted into their derivative stats: Damage bonus, Hit Points, Major Wounds, Power Points, Experience Bonus, and Move. All challenges that do not fall under a skill or any of the subsystems are resolved with characteristic rolls. A Characteristic roll is done using the appropriate characteristic's value, multiply it by five and the result is the percent chance of success. As normal, you need to roll under to succeed. For example strength of 15 would give you a base chance of 75%. However, some more difficult tasks may only have a multiplier of two or less as determined by the GM.
Basic combat involves three phases: Statements, Actions, and Resolution. In the statement phase players, in order from highest dex to lowest dex, state their intent for the round of combat. Next players carryout the intent that they stated in the statements phase. Possible actions are move, attack, take a non-combat action, disengage, parry, dodge, fight defensively or speak. Once actions are taken then resolution occurs. Combat is pretty simple; roll against your skill with the given weapon if you succeed you may have hit the opponent. Once your attack succeeds the target gets the chance to parry (using his weapons skill) or dodge the attack. If the attack is not parried or dodged then damage equal to the weapon's damage value plus the character's damage bonus is subtracted from the target's HP.
While the core rules of BRP have not changed much over the years, there have been several add-on rules and systems. The subsystems included are: Magic, Super Powers, Mutations, and Psychic Abilities. The Magic system works similar to the skill system, each spell has its own skill and a roll against the spell's skill determines success. The difference between the skill system and magic system is that spells also use Power Points. Spells in the magic system must be memorized. Mutations, mechanically, are just special abilities that a character gains as a result of some sort of exposure or genetic tampering. Some act like skills and some are static abilities. The Psychic Ability system is also skill based; each ability is its own skill. Like the Magic system Psychic Abilities use power points but the Psychic system also pits either your POW or current power points against the target's POW or power points. Sorcery uses spells that work automatically without any skill roll except in cases where the spell allows the target a resistance roll. Also Sorcery gives the character more flexibility by allowing them to change their memorized spells day to day. The Super Powers system works by giving the player many, many choices for powers and then giving them the ability to buy levels in them. So while there are many powers to choose from there are also many levels of each and it provides a lot of variation. Players buy powers using their character point budget (based on the character's highest stat) and also by taking on character failings. Most of the major comic book super powers are represented; some use power points others don't.
The book, in total, offers over 35 different optional rules that the GM can cherry pick to customize the system to their game. Several of the optional rules allow you to change the character creation process which is why I didn't cover that section, there just a ton of options. Other notable options are: Skill category bonuses that give character bonuses for high characteristics, Hit locations, Minis & Maps, Allegiance and personality traits. With so many options most GMs should be able to tailor a version of BRP that would suit their game.
Other nice features are a very helpful GM section, mostly stuff an experienced GM would already know but it would be a good resource for new or inexperienced GMs. The creature section gives GMs a pretty good amount of beasties for all sorts of genres. The setting section gives general advice on applying the BRP system to most genres, however, each genre is only given a short section.
My overall impression of the book is that it brings BRP up to the level of GURPS & Fudge for adaptability and utility. While being generic and adaptable is an asset to this game it brings with it the usual problems like being able to do all genres but may only do one genre very well. I think this version BRP probably would be better for gritty fantasy or horror games or cross-genre mixes including either. The sanity system is great and could be included to make a nice dark fantasy game. Combat seems like it may be slow and a bit cumbersome with all the parrying and dodging going on and armor absorbing damage. However, in settings without armor, the system could be pretty deadly like it is in CoC.
I like the magic subsystem and the way spells are skills and I like the way pretty well every one of the subsystems are scalable. That's the name of the game here; make it what you want it to be. The book is a huge mass of optional crunchy goodness and a DIY GM's toolbox. BRP does not show it's age, it seems as good today as it was when I first played it and that is uncommon for the older RPG systems. If you like to play several genres but want to stick with a single system that can do them all, BRP is a good choice that should suit your needs.