While Warhammer 40,000: Chaos Gate – Daemonhunters certainly seems to have given players the XCOM-but-with-space-marines experience they were looking for, those players have been critical of its performance, even on quite high-end rigs. They've also complained about how long your Grey Knight marines can stay wounded for. An unlucky start can lead to a death spiral as you're forced to send suboptimal squads on missions, who then get wounded themselves and join the lengthening infirmary queue.
Daemonhunters' latest patch, Update V, should alleviate some of those issues. It includes an optimization pass on the ship's HUD and all the ornate technogothic objects on display in its various rooms, as well as the combat HUD. Draw distances have been reduced and debris pool loading updated, and with luck all that should help you squeeze out a few extra frames per second.
Balance changes include Grey Knights being "more resilient to becoming wounded in the early stages of the game on all difficulties" as well as recovering to full health after a Purgation Ritual. The cost of the apothecary's healing ability has also been reduced to 2 willpower points. That'll make it easier to keep them standing, and on the lower two difficulties the size of enemy reinforcement groups has been dropped as well.
There are plenty of other fixes and tweaks in the update, including "Helbrutes will no longer do an ungraceful slide when performing a rush attack after a stun." Good for them. Check the patch notes for details of all the changes. A few people are experiencing crashes after this update, so if you're one of them go to Properties > Local Files > Verify Integrity of Game Files in Steam and that should sort it out.
