You can read the full manifesto of Delve balance changes here.
In Delve League existing sources of attack block to spell block conversion are now a flat source of spell block. This change will enable players to have a solid spell block source on any character, instead of simply being overpowered on high block builds and weak on characters that didn’t put any resources in blocking.
Now let’s talk about Traps.. and their nerf. Clearly, GGG thinks they were powerful to the point that they “invalidated other ways of using many skills”. Time on traps abilities will likewise increase as well as damage punishments for Multi Trap Support and Minefield Support Gems. Traps will have higher DPS to make up for the power loss.
Instant skills will no longer have the need for other skills to finish casting, you can use them in conjunction. Also, instant skills won’t work in a frozen or stunned character.
Clearly, a countless number of effects will be instant now, the greater part of which are buffs. Also, a large portion of abilities such as Blood Rage, Righteous fire, Molten Shell, Convocation and Phase Run remain untouched.