Path of Exile is the free-to-play action RPG that just won't stop giving. The release of Ascendancy today at 12pm PT (Path of Exile servers will go down at 9am PT) marks its fourth major expansion, and the patch notes would be capable of filling the sort of dusty, arcane tome you'd expect to find in the Lord's Labyrinth it introduces.
The highlights are the Trials of Ascendancy, the Labyrinth itself, nineteen Ascendancy classes, new Enchantments and the Perandus Challenge Leagues. The Trials of Ascendancy are a sort of deadly training mission set by Emperor Izaro to find a worthy successor: there are six in all, with versions for each difficulty level, which introduce you to the different types of trap you can expect to encounter in the Lord's Labyrinth. Beat all six on one difficulty level, and the Labyrinth opens up in the Sarn Encampment.
The Labyrinth combines all the devious traps you faced in the trials and assumes a new layout each day. You have to beat it in a single life—dying sends you screaming back to the beginning again. The same goes for portalling out mid-run. In the depths, you'll battle Izaro three times and, because he's the awkward sort, the mechanics of the fight not only change daily but between bouts as he learns from your playstyle. By beating him (along with other challenges in the Labyrinth) you earn treasure keys which are used to unlock chests at the end of the dungeon.
Those chests contain more than the standard loot. After beating the Labyrinth for the first time, you can pick one of the three Ascendancy classes that correspond to your core class. From then on, completing the Labyrinth for the first time on the other difficulty levels grants skill points to spend in that tree. Enchantments, on the other hand, are awarded after every successful run.
Finally, if you fancy a fresh start, the Perandus Challenge Leagues boast a set of 40 new challenges in addition to caches of hidden Perandus family treasure (with obligatory guardians) which can be exchanged for equipment and artefacts.
This is a brutal summary of monolithic patch notes, so if you're invested in a particular build or bugfix, you'd better scour the source material to be safe.