First off, a little background information from me, I did not grow up with B/X, Holmes or any original versions of the "world's greatest role playing game". My background is AD&D 2ed. The first thing I love about Blueholme Prentice Rules, is its like 60 pages, a quick and easy read. Having not been entirely familiar with the Holmes version of D&D, I had a few surprises, which I quite liked. Remember I grew up with THACO, and Variable weapon damage and initiative. The weapon speed thing and all damage being d6 only, totally threw me for a loop. But this is the way holmes wrote it, and the way it was faithfully covered in Blueholme. I like it cuz its deadly! But it also can give the hero's a chance. ex 4 PC's (1d6) are up against a dragon, the most damage the Dragon can do is 1D6/1D6 + Breath Weapon. Now obviously if you start off as a lowly Wizard (1d4 HPs) sure you might die in the first encounter. But from what I gather the whole point of Holmes was not so much the hack n slash, but how could the PCs go about getting the treasure without having to always resort to violence.
Another thing that I adore is the same attack table for all classes. This is crazy easy compared to having to look up THACO by Class and Level that I was used to! (2e).
I absolutely love the following:
The layout and artwork
The Monsters (these are all basic monsters, a lot from myth and legend)
The treasure tables (they are easy to use and easy to look up - side note I need a PC with an "Elfin Cloak And Boots"
Blueholme Prentice rules covers levels 1 - 3. Dreamscape design (the creators of blueholme) are presently working on hard on the compleat rules - see their blog for more information on this.