I was always surprised to be a Swords and Wizardry fan. In a lot of ways I was a bigger fan of the original basic and expert (B/X) D&D books released after the first run of Dungeons and Dragons (and contemporaneous with Advanced Dungeons and Dragons).
But the adventures sucked me in: both Grimmsgate and MCMLXII caught the sense of wonder of the early adventures and the lack of systematic approaches to everything that came latter. Modern descendants of the original D&D (both the Wizards of the Coast and Paizo versions, both high quality products) lacked the sense of wonder that can from not fully understanding the world. When everyone knows what an Ogre is and can do then there are few surprises left.
The latest addition, in terms of rules, is Swords and Wizardry complete, which manages to have all of the key elements of the rules in 131 pages or so. Sure some of the elements are not described in great detail (especially the spells) but that is a virtue. I do think it was a mistake to include the spells above levels 5 or 6 . . . but the designer even admits to this in a sidebar.
Overall it was a refreshing vision of the game in an earlier era and one that I quite liked. It was well timed to come out with the re-release of TSR D&D (both as premium reprints and as PDF files). I have quibbles (no elf Druid despite an illustration to the contrary) but I think the vision and the production quality make up for these issues. It is true that the system will work best for those who already understand D&D, but that really was how the hobby came to be (with the rule books often being somewhat inscrutable).
Overall, I have really enjoyed this game system and I hope that Frog God Games continues to do high quality products like these ones (especially the modules).