I started playing a variant OD&D, but never saw the books, just mimeographs of the tables. The first book I saw and owned was Holmes Basic. But unlike many, I can't remember every tiny rules difference of every edition. So what I mainly remember about Holmes is that it was D&D for levels 1-3.
But there are two rules in Holmes I definitely remember and like. One is the rule that extends scroll creation to Magic-Users of any level. The other is Dex-based initiative. I definitely allow 1st level Magic-Users to make scrolls. I don't use straight Holmes initiative, but I do make Dex an important factor, and I don't dice for initiative.
Holmes has had a significant impact on the way I play.