A primary cause of complaints about replayability with the division is the lack of variation in missions themselves, which make up a large portion of the endgame PvE experience. After playing through a mission a couple times, you know when, where, how many and what type of enemies spawn. You can essentially memorize exactly how a mission plays out which lessens the challenge and also gets boring. D2, D3 and others, on the other hand, will randomly spawn (within certain parameters like what enemies can down in what areas) groups of enemies that are varied and have a chance to be tougher and with random extra abilities or modifiers. This helps with relieving boredom despite playing through the same level.

The Underground expansion helped relieve this a bit by generating dungeon maps based on a limited sewers tile set though an issue with that was it got boring fast because it all looked the same. It also utilized the same spawn points in each tile as well so if you played it enough you'd know where enemies would show up though it wasn't always a single possible spawn point and again you'd fall into the maybe unconscious memorization of the content again.