So, is the MV:Nentir Vale better than the 4EMM? and why?
Yeah, the consensus is that it's miles better than any of the 4e Monster books that have been put out. I'm not making the claim it's objectively better than 2e's Monstrous Compendium, but it's the only thing that might come close.
Rather than MC's more encyclopedic approach to monster fluff, most of the Nentir Vale entries concern themselves with specific, unique monsters or with specific groups. 4e's reskinnability makes these stats useful for other scenarios (I've used the city gang before when I needed a diverse and useful set of gang stats), but they've also got a lot of very rich plot hooks and background that begs to be used, stolen, or adapted.
So while you won't find out things like the mating habit of owlbears, you do get some nicely developed characters from a pack of adventurers who became an undead horde. Or a pair of troll (ogre? it's across the room, I'm lazy) brothers who are delightful set of antagonists for any campaign of the right level.
The monsters are all integrated into the default "Points of Light" setting (but still highly portable) and provide a lot of rich fluff and hooks that were missing from earlier 4e monster books.
In 4e, the monster books got progressively better with each book, except maybe MM2 which was as bad as MM(1). Monster Manual 1 in 4e is pretty much objectively the worst monster book that has
ever been published for D&D. MM3, Dark Sun monster book, Monster Vault. By the time they hit MV:Nentir Vale, they had evolved the form -- and learned more than even in the Essentials Monster Vault, which you have -- to the point that MV:Nentir Vale is one of the standout products over the entire 4e line.
Also it comes with the jazzy tokens and a couple maps.