Summary: this is mostly a simplified version of the SRD (a lot pulled directly from that), with additional restrictions placed on many things and optional things (like feats) not used. It has a few pages on building a stronghold or guild and using hirelings. It also has a nice appendices for converting monsters into its system, with an example, and saving throws to ability scores. The format is decent and it has a pretty good index from what I can tell.
Over all, it isn't bad since it is 35% off right now, but knowing what it really is that this point I would rather have saved my money. If you are looking for something like this, I think it might be good for you, as it is a nicely laid out version of the SRD with the changes noted below.
Here are the main differences and similarities after a quick read through. You'll see that the general mechanical concepts are retained from 5E, this work is more about restricting and somewhat simplifying options than anything else IMO.
Only 4 races, Dwarf, Elf, Halfling, and Human. ASIs are diminished to a single +1, humans get two +1s. Speed is Normal for all (see below).
Most importantly, this uses Class Restrictions based on race (no Clerics except humans, all Fighter, most Thieves (Dwarf is limited to Fighter/Thief, cannot be full Thief), Elf and Human only Wizards).
Only 4 classes: Cleric, Fighter, Thief, Wizard. Limited to level 10. Each grants a +1 ASI to their main ability score.
Hit Dice are lower (Fighter d8, Cleric d6, Thief and Wizard d4).
Backgrounds determine what you can add your proficiency bonus to outside of combat. This replaces skills. Subject to DM fiat.
Only 3 alignments: Lawful, Neutral, and Chaotic.
Only copper, silver, and gold for coins.
Only leather, chain, plate, and shield for armor. Always add DEX, no limit.
Simplified/reduced lists for weapons and equipment.
Simplified/reduced spell lists.
Cantrips (and Orisons for Clerics) are general, minor spells, subject to DM fiat as to most usage. Individual cantrips are gone.
DCs are only Easy (8), Normal (12), and Hard (16).
Ranges are Close (5'), Near (30), Far (120), and Out of Range (over 120).
Movement is Slow (15 feet), Normal (30 feet), and Fast (45 feet).
All monsters use d8 hit dice.
Monster XP value is lower, much so at higher CRs.
But CR values are altered. For example, a Basilisk is CR 8 here, instead of CR 3 as in the MM for 5E.
Uses 5E-style multiclassing, up to 10 levels total.
Not really. Both lines were very successful until Willaims decided to run the company into the ground with her vanity Buck Rogers game (as well as getting absolutely destroyed in the Card Wars). TSR published a lot of games over the years, some successful and some not, but was undeniably a successful game company for a long time. There's a reason why people still play B/X and BECMI, and it isn't because it/they was some shallow, lesser version of AD&D.
I was a BX / BECMI player and wasn't a fan of AD&D so I hear what you're saying.
But ... let's not forget that the only reason that there was a distinction between "Dungeons and Dragons" and "Advanced Dungeons and Dragons" in the first place was because Gygax wanted to screw Arneson out of his royalty payments by claiming that AD&D was a new and different game. The original Basic game as written by Holmes was supposed to be both a lead-in and a cleaner explanation of the white box content. That's the function that the Essentials box has now.
And also honestly? The 5e game is actually a super-simplified game in the grand scheme of things. The disparity in complexity between D&D and AD&D was huge if you played AD&D as written (which nobody I knew did of course) so a simpler version of the game made sense. Because of how modern games are designed I'm not sure what you'd drop out of 5e to create a "Basic/Expert" track for the game other than reducing the number of character classes, subclasses and spells available to the players.
The complexity in 5E comes primarily from its excess of moving parts, primarily in the form of classes and races, especially where "splat books" are concerned. It isn't nearly as bad as 3.x era games, of course, but it is still cumbersome without much value to actual actual gameplay. Its "skill system" such that it is is simplified to the point of almost not being worth discarding, except I honestly think games that are intended to challenge players' creativity are better off without them.
5e has both a Basic type line (Basic, Starter, and Essentials) as well as the normal line.
It essentially (hahaha...okay...maybe you don't see my pun there) has two lines going.
It's more pronounced in 5e than any other edition previously since WotC took over.
3.X had it with their Basic D&D, but that only went up to level 3.
Basic D&D in 5e goes up to level 20 for 4 classes if one wants to stick to Basic. The Starter box goes up to level 5 and the Essentials box goes up to level 6.
I'd say a HUGE reason for 5e's success is actually DUE to having two lines.
It follows the same reason why TSR D&D had 25 million players...it is BECAUSE of these two lines that it meets it's success.
When they dropped the two lines TSR D&D ran into massive trouble (yes, I know other reasons are listed for it's failure...but there is that thing where sales dropped off after BECMI/RC was dropped by some anecdotes).
Two Lines following the Basic/Advanced idea I think are essential for a greater amount of success.
It also is essential that they are largely compatible (sure, some can point out many differences between B/X, BECMI, and AD&D, but let's face it, they are mostly compatible and there are a TON of players that went from the B/X and BECMI to AD&D).
This is one of the core items I consider why 5e is successful and why I support the idea for an Essentials Kit building off the Starter box and a Basic ruleset online.
It introduces new players to the game without that sense of overload. It makes it so that they can have their alternative if they like it (basic pdf). It ALSO means that they now are familiar with the rules and I feel MANY who start on this path eventually start playing the full 5e game. Just like B/X and BECMI got a TON of gamers playing AD&D, I feel the Basic line of 5e does the same thing.
There IS a split of the line with 5e between Basic rules and the full rules, but I think it BENEFITS 5e and has brought in FAR MORE gamers to 5e and buying 5e books than any detrimental effects people think two lines bring (just like BECMI did for AD&D).
The current Basic line (Starter Box, Essentials Kit, Basic Rules) actually has MORE core rule supplements than Holmes (1) or B/X (2) did. It has less than BECMI (5) did, but I think that the OPTIONS available for various race and class combos actually make it so that there are MORE options of playable classes in the core rule sets (but only if you include the Basic PDF probably, though essentials comes close if not more overall as well).
So, I think there actually ARE two different lines of 5e right now, but just like B/X and BECMI complimented AD&D and made the brand stronger, the split actually makes 5e stronger and sell better as well.
PS: Just ask most BECMI players as well as B/X players. I bet you'll find that almost all of them (though I admit, there are a few holdouts) also played AD&D. The same eventually goes for those who play the Starter Box, Essentials Kit, or the Basic PDF...eventually I feel those that stick with the game also go one to buy at least some of the core rule books and some of the supplemental rulebooks.