There is something to be said at starting at the beginning, and that's just what I'm going to do with this part of the review of Blood & Treasure - Races and Classes (or at least, touch on classes), as they work hand in hand.
First things first - it's the usual 6 stats, and bonuses and penalties run the usual stretch - -3 at 3 and +3 at 18. It was nice to see which saving throws a high Dex gives a bonus to, as I usually just winged that part based on common sense. It should also be noted that stats give bonuses to task rolls (think skill rolls). So Dex may help you open a lock but Wis will help you listen to that locked door.
Races: The same ones from the AD&D 1e Player's Handbook. Humans, Dwarves, Elves, Gnoes, Half-Elves, Half-Orcs and Halflings. If you wanted to run a game emulating the OD&D Boxed set, you would omit the races designated with a [A] for "Advanced". Things are designated thus throughout the rules, so you can set a virtual switch of what stays in your game or not. The other designation is [E] for "Expanded".
Now, as far as I can tell, any race can be any class, which obviously is the first thing you'd house rule if you were going to emulate an earlier edition of the game. That being said, John built in some niche protection for the races. Humans get a 10% bonus to expo, which is huge. They also get a free feat (if used) or +1 to all saves if feats aren't part of your game (they are not really 3e feats either, but that's a whole 'nother post).
The demi-humans get their niche protection in their multi-classing, which is determined by race. For example:
Dwarves can multi-class as cleric/fighters, magic-user/fighters or fighter/thieves.
Half-Orcs can multi-class as assassin/clerics, assassin/fighters and assassin/magic-users (or if they single class, they can dual class later like a human.
See a trend? Every demi-human race has a set of 3 multi-class combinations, and each combination has a preferred class. Nice way to take care of niche protection. Before you ask, halflings have thief as the preferred class.
Classes share one of three experience point advancement tables. Multi-classed characters all share one table, no matter the class combination. It certainly simplifies things. I like it. I like it a lot.
Alright, more on classes tomorrow - I've rambled enough for tonight ;)