Currently Pokémon Go's Pokédex covers the first 384 creatures introduced to Nintendo's collect-em-up series, up to and including the third generation of games. Developer Niantic has announced that Gen 4 creatures will arrive in the game soon, which is not the biggest surprise in the world but pretty exciting for Go-lovers.
As a Pokémon Go player who's two creatures away from completing their first two generation collections, adding more creatures brings back some of the excitement of seeing new creatures regularly to the game. Even better, it introduces the final evolution stages for a number of early series creatures. You'll be able to soon start evolving Gen 1 monsters like Magneton into Magnezone, which will likely offer utility to those huge stacks of Gen 1 candy any long-term player has sitting around.
On top of this, Niantic also announced a series of upcoming changes to the way Pokémon Go works. Some of the most notable include: weather now has a reduced effect on which creatures spawn; the Pokémon which appear in an area will now change over time to freshen things up; and areas marked as parks or nature reserves will now feature a wider variety of rarer creatures, somewhat akin to the Safari Zone in the main RPG entries.
Beyond this Niantic has said various Pokémon's combat power values will be tweaked for balance. The gap between high and low HP creatures will be closed; high defence creatures will have their stamina rebalanced to make them more viable for gyms; and creatures with the highest defence values are also going to see those reduced a little.
The changes to the ways creatures spawn sounds especially good (on paper anyway), but until the update actually lands it's tough to tell whether it will be an overall positive for the game or not. But the introduction of Gen 4 is exciting, and feels like it's happening at the right time.