You can check the official Patch Notes for Delirium 3.10 here.
TL / DR
Animate Weapon, Artillery Ballista, Shrapnel Ballista, Kinetic Blast, Power Siphon, Ballista Totem Support, Unleash Support and most travel skills. All Totems and Ballistas have had their base Life increased by up to 50%.
Although Bladefall, Ethereal Knives and Blade Vortex did not get numeric changes they are passively buffed via the addition of the new Blade Blast skill. Other interesting things that can be mentioned is that reductions to Reflected Damage will now also affect your Minions. In addition to that there will be a ton of new monster types that can be raised as Spectres.
Bone Barrier got nerfed by a considerable amount, Commander of Darkness now provides 30% Resistance instead of 20% (not a big deal).
Ambush and Assassinate / Opportunistic got slight numeric buffs while Mistwalker got 5% less Attack and Cast Speed while Elusive.
Radiant Faith got a well deserved 50% nerf.
Items changes and what to keep an eye on
Crown of Eyes is now once again a viable chase Uniques for certain builds, DO NOT VENDOR IT! Chains of Command got hit hard with the Animate’s base duration fixed at 20 seconds. For a comparison the regular Animate Weapon will have a base duration of 40 seconds. Shaper's Touch are now 50% less effective for Strength-stacking builds. The Baron got hit hard with the nerf hammer too. Doryani's Fist got buffed by a great deal. Other unique items got buffs and nerfs but not of big significance.
Fossils ruled the crafting Meta for long time and this is changing now. Almost all Fossil-specific mods are moved to certain Conqueror Influences, with the exception of Faceted Fossil, Bloodstained Fossil and Hollow Fossils.
Spawning Conquerors on the Atlas is now more deterministic. Sirus has been buffed by a good amount. Many improvements have been made to Incursion Temples. Vaal Side Areas are now more challenging and rewarding. Most of the bosses in unique Maps have had their Life increased significantly. Shaper cannot be one-shot, he got the Brine King treatment (reduced damage taken in the first seconds of each phase).
These are some of the most important changes coming in Delirium 3.10. You can also check out Furty’s