You may not have been expecting a new version of Essentials, only seven months after the previous one, but surprise! Not only is it being released so soon (compared to the gaps between previous releases), but it's a very important step forward.
Before we get into it, I should say that Essentials is now open source on GitHub, and this has directly helped others to contribute to the development of Essentials. I wouldn't have been able to do all this by myself. Everyone who has worked on Essentials with me is fantastic, and I want to give them a lot of thanks for it.
But anyway, what's so great about v19?
mkxp-z ftw omg
mkxp-z is a bundle of letters, but it's also a very big deal. It's an alternative to RGSS, and if you don't know what that means, it's a set of code that RPG Maker games can use to make themselves work. And not just work, but work better than they would if they were using RGSS. RGSS is, to use the technical term, way old now, and mkxp-z is much newer and faster and has more features. And it's now in Essentials.
The upshot of it is that Essentials should now work a lot better. For one, it's faster, but that's not the only benefit. Fonts can be used without having to be installed, there's a built-in way to remap the controls to whichever keys you want, you can access information on https websites (so Mystery Gift works again), there are better screen resizing options, custom loop points in music, and so on and so on. It's also possible now to create versions of a game that can run on Linux and Mac, so games are far more portable now.
Sounds exciting, no?
Scripts and values
There have been various code enhancements behind the scenes in addition to the above, and one of them is the addition of support for external scripts. These scripts will live in the new Plugins folder, which makes it much easier for you to add third party scripts to your game - just drag and drop the script files.
Another big change is that things like species, abilities and items are now going to be known by their internal names (:BULBASAUR, :INTIMIDATE, :POTION, etc.) rather than their ID numbers. This applies to storing them in variables such as Pokémon objects, as well as using them in the filenames for sprites and icons and cries. The meaningless numbers will be abolished completely in future. Lots of code has been changed because of this, and Pokémon/item graphics have been rearranged into different folders to make them easier to work with.
How about something that makes more sense? There are two new PBS files (regionaldexes.txt and ribbons.txt), and tm.txt has been merged into pokemon.txt/pokemonforms.txt. Also, encounters.txt has a new format which offers increased flexibility and even allows multiple sets of encounters per map to choose from, so you could make wild Pokémon get stronger as you earn more Gym Badges (for example).
Big and beautiful
You know how events occupy a single tile no matter how big their graphic is? Well, not any more! You can now specify the width and height (in tiles) of an event, and that event will sit in all of them. There are so many things you could do with this simple yet powerful feature, such as having huge boulders to push around, Snorlaxes blocking whole paths at once, condensing the contents of whole bookshelves into a single event, triggering a single Player Touch event that lies across the whole of a road, and so on. Why use many events when a single one works just as well?
Meanwhile, the overworld weather animations have been overhauled and now look much better than they used to.
And the rest
To be honest, a lot of what's in v19 is behind the scenes - code improvements and refactoring and restructuring. It ought to be very exciting to those who are interested in that kind of thing, but on paper it's not as flashy as a pile of new features would be.
Despite that, there are still a number of new things in v19 that everyone can appreciate, and of course there are always bug fixes. The fact that so much work has been put into the gears and levers behind the scenes probably makes makes it an even smarter idea to upgrade your game to it. It's an important milestone for many reasons (mkxp-z, code restructures, being the first result of the new open source development), and exciting times are ahead.
The full change log for this version is available on the wiki.