[Update]: The Binding of Isaac's gigantic Repentance expansion is set to launch in late 2020.
The Binding of Isaac: Afterbirth+ arrived on January 3rd with ~100 new items, a final chapter along with a new boss, new challenges to undertake, and a variety of other features. Unfortunately for the folks over at Nicalis the extremely well-made community expansion The Binding of Isaac: Antibirth arrived ahead of Afterbirth+ and completely overshadowed it in both content and quality.
However, while Antibirth might have a bigger set of features Afterbirth+ brought with it perhaps the biggest addition Isaac has ever seen - official mod support! As of right now the Isaac Workshop sports thousands of fan made items, characters, balance changes, cosmetics, and the list goes on. While having that many mods available for download is a great thing indeed, its also a bit of a hassle to sort through all of them in order to find the truly excellent ones.
The developers were seemingly well aware of this little problem as they have recently unleashed an update that not only added a couple of official items into the game, but also a whole bunch of fan made ones as well! You can find the full list of items, as well as what they do, over at the official website.
As for the future, Edmund McMillen is currently looking for mods that add new challenges with unlockable items, as well as tricky bosses and enemies. But perhaps most importantly, in terms of gameplay balance anyway, he is also looking for new Angel Room items to hopefully make that part of the game more than a simple waste of time when compared to the Devil Rooms.
If you know any quality mods that fit this criteria, or if you've even created one yourself and feel like it would be a great fit for Afterbirth+, you can contact McMillen directly via Twitter.