I read the 4e DMG, cover to cover. I was not terribly impressed.
I haven't read either the DMG2 or the Essentials equivalent. By the time they were published, 4e had passed me by.
To be honest, though, the standard for DMGs is actually shockingly poor.
The 1st Ed DMG is a badly-written mess, with parts that make no sense at all (initiative). The appendices, however, are spectacular.
The 2nd Ed DMG is almost completely worthless, with only the magic item descriptions holding any value.
The 3e DMG (and 3.5e version, and Pathfinder's DMing chapters) is okay, but incredibly dull. We really, really don't need several pages of description of different types of door!
The 4e DMG has some good advice, some really bad advice, a couple of faux pas, and almost no value after that first read-through. All of the crunch has now been rendered obselete, and it doesn't have even the magic items of the 2nd Ed version. It's one to borrow, read once, and then never reference again.
Surprisingly, the very best DM book I've encountered is the DM's booklet included in the BECMI Red Box. Probably due to the reduced page count, it is forced to get to the point, do the job it sets out to do, and then end.
Of the "second DM books", I'll hold up the 2nd Edition "Campaign Sourcebook and Catacomb Guide" is being the high-water mark. Frankly, the contents of this book should have been in the DMG, and it's almost inexcusable that it was not.
The 3e DMG2 has some good advice, but really came into the product line far too late - by the time it came out, almost anyone who would benefit from it probably knew it all by then.
As I said, I haven't read the 4e DMG2, so can't comment.
Finally, the Pathfinder "GameMastery Guide" is excellent, and well worth a read-through (even for 4e DMs). The only hesitation I have in recommending it is that I don't know how far it overlaps with the 4e DMG2, so it might be redundant. It's not quite as good as the CS&CG from 2nd Ed, but it's not far off.