In a word: Awesome!
I'm extraordinarily happy that Wizards of the Coast has decided to walk this path. I'm almost certainly going to buy the Player's Handbook [done], Monster Manual and Dungeon Master's Guide [because that's just what I do…], but it is fantastic that the option exists to hook new players in.
Now for the quick critiques. I haven't digested all of the new DM Basic document (essentially the Mini Monster Manual) but I have noticed a few oddities that I thought I'd mention.
"Adult Red Dragon" is at the beginning while "Young Green Dragon" is at the end. I'm hoping this is not a trend that will be continued in the Monster Manual. Monsters that are variants of the same type should be grouped together, especially if they are of the same color. I don't want to find "Young Red Dragon" at the end of the Monster Manual 300 pages distant from "Adult Red Dragon". Now, if "Red Dragon" were in "R" and "Green Dragon" were in "G", I wouldn't like it, but I could perhaps accept that. At the very least, though, the different age categories of a particular Dragon type should be grouped together. Young, Mature, and Adult dragons should appear on the pages adjacent to each other.
I also preferred when groups of monster variants shared a page in the old Monster Manuals - like Rats, Rat Swarm, Giant Rats, Dire Rats, etc. With all the stats grouped, one could combine an encounter of similar creatures that might lair together and have almost everything you need in 1 or 2 facing pages. I prefer this over the current first word alphabetization that spreads all the vermin across the entire book. I prefer "Rat, Giant" or "Snake, Giant" over the current method because this naturally creates these groupings of similar creatures.
Similarly, Giants are spread out rather than grouped. This bothers me less than Dragons since they are distinct monsters, but I still liked how the old books grouped them so that you could browse through Hill Giants, Frost Giants and Fire Giants while comparing stats all in a few pages
Missing Hoard of the Dragon Queen Monsters
For some reason, many monsters in the HotDQ PDF are not included. This makes it more challenging for DM's who want all their monster stats under one [metaphorical] roof as one would have to print the PDFs back to back without alphabetic order (and some redundancy between the two documents). It'd be nice to have iconics like Otyugh and Roper on the proper pages.
This may have been due to expediency. Perhaps the pre-Gen Con release of the DM Basic Rules precluded the possibility to get in the HotDQ stats into the new PDF, but it's still a bit puzzling since both of these documents have been released for free. I'm hoping this will be corrected in a near future update. I do wonder if this has something to do with protecting sales of the Monster Manual by not including some monsters in Basic, but that seems silly since both PDFs are in the wild for free.
I was a little surprised to find Dinosaurs included. I think it's neat for those that may want to run a "stone-age" or Land of the Lost style campaign, but I'm a little surprised that these were include over other possible selections. This isn't so much of a critique, because I'm not particularly negative about it, but more of an observation. Also, Dinosaurs are not grouped together due to the alphabetization I noted above.
No Owlbear Hug Attack
Seriously?!? No Owlbear hug? What game are we playing here? :)
My first monster house rule: When the Owlbear succeeds in both claw attacks, as a bonus action it is allowed a chance to grab on the same turn with constriction damage on the following turn(s).
More to come as I dig in…