For new players this might seem like the best thing ever. I have to admit I had some reservations about going from 2E to 3E with my players but they were all dying for it so away we go!
I suspect this review will be of more use to veteran types than novice types, as the latter have no comparison, but here goes:

THINGS I LIKE ABOUT THE 3E DMG

(1) WORLD BUILDING: the 2E DMG didn't have this aspect in it. You had to get one of the supplementary sources to figure out all the things that are now in 3E. Good step.

Howeer, let me point out that 1E had the best context and advice for building a world. I would say that if you want advanced techniques for world building to seek out that DMG as well as the 2E CAMPAIGN SOURCEBOOK.

(2) NPC CLASSES: it was always a hassle trying to make the queen tough enough to not be killed by one sword blow. To do that, you had to make her into a class and most of the classes didn't make much sense for someone who never got out and was in court.

Now, there are artisan classes, like a 20th lvl blacksmith, and the aristocrat. It includes usual skills and such as well as the die to use.

Great idea. Now, I don't have to make the court queen a 15th lvl thief to keep her alive.

(3) PRESTIGE CLASSES: a cool idea. These are organizations of very tough or unique people who have special powers.

BTW, for you 1E players, the assassin is now a prestige class. Glad they brought it back.

(4) RUNNING THE GAME: again, this wasn't in the 2E DMG; it was in the sources mentioned above but overall, this is great for new DMs. The book helps you describe events like one of story rather than just numbers.

(5) ENERGY DRAINS: PCs now get saves against undead hits. That was always a bummer to PCs in previous editions.

(6) COOLER PICTURES

(7) NEW MAGIC ITEMS: not seen in the usual 2E books;

(8) WAYS TO TONE DOWN DEMIHUMANS FROM BEING ANY CLASS: if you're a 1E and 2E purist like me.

(9) DC EXAMPLES: very helpful if you need a quick number for skill check.

(10) RESULTS OF HAZARDS: better details than in 2E; had to get this from supplements or make it up.

WHAT I DO NOT LIKE ABOUT THE 3E DMG

(1) MAGIC ITEM PROTECTION CROSSOVER: in the 1E and 2E rules, you couldn't combine magical armor and magical rings. No longer true. Now, you can wear both which can upset game balance potentially. Still exploring this issue.

(2) XP FOR MONSTERS: you can go up a level for every 2 sessions if you kill enough things. To those who want to give out xp for RPGing and other matters, I suggest you use the optional rule that tones down all monster xp by half.

(3) PRESTIGE CLASSES: it should be a lot harder to get into these since they're so powerful. Otherwise, wouldn't everyone do it?

(4) TRAINING FOR XP: I know this isn't popular with some people but I find it hard to believe you shoot up a level just b/c you got 100 xp for killing that creature.

If I want to teach myself tennis, it's true that I can do it to some extent by watching others and emulating them. But, at the same time, there are certain bad habits I pick up that will have to be unlearned and spotted by a good instructor. I know lots of people who play tennis with weak backhands and try to play around it. Works well with other people who have such weaknesses but you get killed against other players who slam the ball down to your backhand all the time.

(5) CRITICALS: in the old rules, only the die was doubled or tripled and then the bonuses were added. Now, you total all the bonuses and double or triple it. Personally, I think that has the potential to kill a lot of PCs but my players want to play with it so they'll regret it soon enough. :)

(6) OVERLAND TRAVEL: this isn't listed as it was in the 2E DMG. From it, you could figure out how long it took to get to certain places. Important during downtime especially when PCS are going all over the place.

(7) SPELL COSTS: 2E listed some popular spell prices; not in 3E; bit of a turn off.

(8) LESS INFO ON HIRELING COSTS AND SUCH: more details in 2E if you wanted to hire people for your castle or get soldiers;

(9) NO TERRAIN COMBAT DETAILS: the 2E has more info on underwater and aerial adventures if that floats your boat.

(10) EQUIPMENT LIMITATIONS BY MEDIEVAL DATE PERIOD: in 2E, certain things didn't exist if you based it on Historical models. This was for a good reason. For instance, plate armor probably wouldn't be around if you wanted to run a dark ages campaign and, if it was, then you would have some really powerful people around who would be harder to hit.

(11) SOME MAGIC ITEMS MISSING: in 2E, there were a lot more. Not in 3E but maybe the missing ones will come out in a supplement.

(12) LACKING IN NEGOTIATION AND ROLEPLAYING: this really isn't a problem with 3E but D&D overall. When I was younger, hack and slash was the way to go with a few puzzles and tricks. But, that got old and broke up our group for a while. When we came back, I kept those elements but factored in more of a mulitilayered plot story with context, History and more roleplaying.

(13) SOME GREAT MATERIAL LOST: RAVENLOFT belongs to WHITE WOLF now; couldn't handle the extra work or cutting back? Also, unknown of PLANESCAPE and several other realms that may no longer be used in 3E. Big bummer as many of them were good. I especially liked PLANESCAPE even though my campaign wasn't in PLANESCAPE.

Anyway, my advice to old and new RPGers is to consider some points I rised. It's a lot easier to change things now then later when players are used to certain rules. Whatever the case, some things are good and some are not in my opinion.

To the more seasoned people, hope this helped some. :)