Ah I see. This was 2nd Ed era. I am not too familliar with 2E product beyond the core release (played GURPS during the 90's)
So what type of rules did it feature? Was it the core 2E rules for low level only or a special rules-lite version?
It was a stripped down 2E rules with just the first few levels. Ftr/MU/Cleric/Thief, IIRC. It did have pre-gens, but I do believe it had some basic character creation rules.
The DMG portion had DM rules, and a couple or three small adventures.
The MM had your basic critters. Orcs, Goblins, Skeletons and the like.
I'd say each book was probably around 32 pages. And it came with plastic minis for the characters, large scale dungeon maps for the adventures, a DM screen with all the necc tables, dice, and a CD that you used during the adventures. If you are familiar with first 3.5 basic Set (black dragon), it was similar to that.
FWIW, the 3.5 set (at least the one with the black dragon) is a pretty decent attempt at a basic set IMO. It has pre-gens but also covers creating your own character (F,R,C,S) with basic feat and spell options for the first 2 levels, and like Mentzer it has an introductory type Dungeon level (not solo), a slightly larger keyed version, and then another area for the DM to do his own thing. Still nothing on the level of those old Basic sets, but a neat box. I think sans minis and adding counters and some added page count (and a bare bones DM screen), it would have been quite good.