Blizzard really picked up its game with Diablo III's 2.0 update and each major patch since has continued to deliver the goods. 2.4.0 looks no different, promising a new zone, expanded areas, extensive set piece revisions and more.
The official overview over on Battle.net does a good job of covering everything coming with 2.4, so we'll just go over the bigger changes here. First off -- there's a new area called Greyhollow Island. It'll be available via Adventure Mode and looks suitably dark and creepy in typical Diablo III fashion.
Next up is set pieces. With 2.4, Blizzard is taking the opportunity to revise almost all 24 available, with the objective being to not alone bring them up to par, but to provide players with a reason to use new combinations of skills and runes.
And of course, it wouldn't be a post-2.0 Diablo III patch without tweaks to rifts. In this case Blizzard is adding "empowered" rifts, which will allow players to trade gold for the chance to get more Legendary Gem upgrades at the end of a run.
All in all, it's sounding like a chunky update. Hit up Battle.net for the full breakdown.
PATCH 2.4.0 PTR PREVIEW [Battle.net]