This is certainly a solid OSR entry. It includes everything the prior reviews about content is true. In case you are not sure, this is the equivalent of the DMG + the Monster Manual. There is solid randomizers and recommendations for randomly generated dungeons, NPC encounters, wilderness encounters, 300+monsters, hundreds of magic items, etc. There is better advice here than in most OSR products I've seen. Certainly, it is a better than the original 1e DMG in organization, rules clarity, inspiration, and it includes monsters (obviously a necessary piece in order to play). It's better than the 2nd ed DMG as well, in that the 2nd ed version didn't have anything for dungeon creation, much less for inspiration, inferior organization, and again MONSTERS.
That said, I don't really understand the hype for this product. The OSE Advanced Fantasy Player's Handbook is really where this system excels. Ifl you have a prior version of the 1e DMG and the Monster Manual, there's not a huge amount of improvement here. You could just run OSE with the OSE AF Player's handbook and your old books without an issue, if you wanted to save a few bucks.
If you dumped your old B/X or 1e books already, or never had them, this is a fine way to go. Just be sure to get the OSE AF Player's Handbook at the same time.
[4 of 5 Stars!]