I found this thread looking up old games I used to play. To understand my perspective I'm 40ish and last played regularly 20+ years ago. AD&D was current when I quit, and I didn't realize TSR wasn't still around and hadn't heard of
WOTC until a year or so ago.

So when I say D&D I'm talking basic, expert, and advanced D&D.
My buddies and I played BMG in high school in Topeka. Even played a few times with Bill Underwood
DMing, and had the opportunity to discuss aspects of the game with him on several occasions. We preferred it to D&D, because it dealt with many inconsistencies that drove us nuts. once we started playing BMG we never went back to D&D (at least when i was playing). I would call it very D&D like/inspired, but it's not a
d20 system.
For instance I remember talking with Bill, and him saying there must be +1 sword factories somewhere in D&D land as they were all over the place, yet it took a fairly powerful magic user to make one. In BMG a beginning mage could enchant a weapon to be +1 temporarily, and by 4th level make permanent +1 weapons.
We also liked the mana point system for spells better than the memorize and forget method.
I found D&D clerics and religion to be hard to ref. In BMG characters have a Morals score where zero was neutral, a neg score was evil, and a positive score was good. It was modified by the PC's actions at the
DM's discretion. Do something bad get -1. Do something self sacrificing get +1. If the PC relied on powers from a God they had to stay in the right range of Morals to retain their spell powers. A PC's morals might influence whether or not their god would offer divine assistance.
The combat system was a little more complex than AD&D, with dodging and parrying, and different hit locations. But it stilled played pretty fast.
I've still got my copy, 2nd edition I think, although it's in horrible shape: duct tape binding, pages falling out. This isn't so much from over use. It fell apart pretty quickly after purchase. My friends and I all had Xerox copies in three ring binders as it was pretty much impossible to use the original book with all the pages falling out. I still have my binder too. I heard that other printings were more durable, but all the books I saw were falling apart.
As mentioned above it has paired stats. STR & CON, INT & WIS, DEX & BOW (bowskill), CHA & PA (personal appearance), and WP (willpower) all by itself. Roll a 1d6 common die for each pair, then add 2d6 to each stat. This was to make it impossible to have a guy with 18 STR and 3 CON and such. If a stat was 18 roll 1d6-3, and add it to the stat if positive.
It has Stamina and HP. Stamina was sort of like dodging. It only applied to targets who knew they were being attacked, and could dodge out of the way. Giant lumbering creatures didn't have Stamina. HP was real blood letting. When you ran out of Stamina or were surprise attacked you started taking real HP dam. Stamina healed quickly. HP much slower.
The classes were:
Warrior: typical D&D fighter
Thief: typical D&D thief
Elf: sort of thief - mages
Dwarf: typical Dwarf
Forester: like D&D ranger
Enchanters: magic user with spells that control beings
Arcane Lorist: D&D magic user
Nature Lorist: D&D druid
Illusionist: D&D illusionist
Elementalist: pick one of the 4 elements, and the spells reflect it
Necromancer: necromancer
Shadow Mage: thief - mage
Priest of Exonerous: like a paladin warrior - mage, Exonerous was the king of Gods, chivalry, purity in battle, etc...
Priest of Sautarius: mage of light, Sautarius was the sun goddess daughter of Exonerous
Priest of Rashok: Rashok was the evil son of Exonerous
There are some other gods mentioned. Thaug was described as the god of Death and necromancers. Some shadow mages worshiped Shadur.
There are some other classes mentioned in the stat and charts, such as Barbarians, but my book doesn't have an actual description of such a class.
The rules cover most everything needed to play. There are some discrepancies and loose ends, but overall a complete system. Half the book is the magic system and spells.
A quick look at Realm of the Powers and I see some fundamentals that look familiar, but a lot of new stuff.
BMG is a pretty cool game, but I don't know about $100. Then again I'm much more into playing than collecting. Hopefully Bill can figure out a way to distribute a pdf or something. I'd love to get his ideas on the realm it took place in. There are some neat ideas in the book, but I remember hearing Bill mention a lot of cool stuff that wasn't in the books when we hung out and talked with him. If there have been revisions I'd also like to see those. Bill impressed me as someone who really thought things out.