I feel like customization in D2 is way too restrictive. There are so many factors that go into why, but I want to go over the big ones.
1) Shaders being consumable, given a price tag to apply, and hidden behind loot boxes kills what they used to be. Before, we used to be able to swap armor without having to worry about being mismatched, or swap shaders without having to worry about having enough of the shaders themselves or glimmer. It takes away the freedom of customization.
2) Everything is dumbed-down. Subclasses have only two trees to pick from, everyone's weapons are the same, and there's no uniqueness to armor anymore. What's the point in farming for the Raid armor when it's functionally the same as every other Mobility piece? You're never truly unique in this game.
3) The current loadout system limits who you are as a character in-game. In D1, you could rock an Auto Rifle, Shotgun, and Sword to be the ultimate close-quarters badass. Now, you can choose between two Primaries and a "Power" weapon. There is no real archetypes you can make for yourself anymore. And with Special weapons now considered "Power" weapons, many weapon types are hardly seen anymore.
4) What's the point in collecting shaders, armor, weapons, etc. when you don't have the space to store them all? I held onto every Legendary and Exotic I could to experiment with later, but my vault was full before I hit 305. And now, I have to sacrifice more stuff to make room for Season 2 stuff.
5) Which sucks, because I won't be able to obtain ANYTHING I'm about to get rid of ever again, because after Season 1 ends, they're being removed. It creates a scarcity scare, where I want to get it before it's gone forever. But at the same time, it's like, why did I even bother with collecting in Season 1, and why should I bother with collecting in Season 2, because the exact same thing is going to happen with Season 3.