I literally got the Delving Deeper preview PDFs a few minutes ago, browsed through them, and must say that I made a mistake. These look good. Seriously. I don't understand what purpose they serve (still), other than to duplicate the original D&D boxed set. But they're nice, no doubt about it. From what I can tell, it's basically LBB 1-3 with some Greyhawk thrown in. I do like OEC from Goblinoid, but think it needed to be a complete release. I dislike Swords & Wizardry because it implements some things completely different from OD&D. Delving Deeper is like an expanded OEC, and it's good.
So, basically, if you want to play OD&D get this. Again I DO NOT UNDERSTAND WHY YOU WOULD WANT TO PLAY OD&D, but hey, that's your decision to make.