Crucible is an apt name for EVE Online's 15th expansion, considering that the game, its developers, and its players have gone through a severe testing this year in many respects. CCP is hoping that Crucible will be better received than its previous expansion, Incarna, and is hyping it as "EVE reforged."
Today Crucible is coming to the game as a free expansion following a period of extended downtime. It's very much a "kitchen sink" update, with major improvements and reworkings of game systems. These include items as big as improved space visuals and dilating time to allow for large fleet battles to touches as small as contrails, an improved font, and new Captains Quarters. New ships in the expansion are a given, but ground-bound pilots might be attracted to opening up their very own customs offices to tax planetary businesses.
There are so many additions and changes, in fact, that it's almost futile to try to crush them into a couple paragraphs, so while you're waiting for the game to come back up, make sure to check out the patch notes, the EVE Online: Crucible website, and our own Brendan Drain's thoughts for more info.