Many players found that the Delirium content becomes extremely hard after a certain threshold. For example, you clear without any problem up to x3 rewards and then you just fall over to a random magic monster. In the Delirium Manifesto GGG’s Devs comment on how they will revisit overtuned monsters. Reward bars will fill up more quickly as you fight monsters deeper and many of the nasty debuff’s duration will be significantly shorter. Monster on-death effects are currently occurring on random, meaning each monster has the chance to leave an explosion on the ground. This will most likely be moved to a pack-based mechanic, meaning each monster pack will have a certain amount of on-death effect, making the mechanic more consistent.
Delirium is an amazing league but it has bad synergy with old game content, simply because when you start the encounter you want to clear as much as possible. Finding something like Alva will most likely make you skip her and keep clearing and back tracking is no fun for any one. This is why the Delirium encounter’s duration will be increased when you find another piece of old content.
Delirium also introduced a lot of performance issues. GGG comments on how fixing that is a main priority at the moment. Visibility in the fog will also see some improvements and finally we will be able to add a keybind to end the Delirium encounter.