basically, it's a bunch of runewords, unique items and cube recipes that exist only in ladder. Usually, players on NL are already very rich and have all the gear they need so they won't be looking for actually making a Grief RW for an example, they can just trade for it. Also, item selling websites are much cheaper for NL than they are for L so that's another way to get everything very easily.
The thing about NL is that it still has very old items like bugged eth tal armor for an example. Items that no longer exist, or exist but in a different version. Those items are typically very expensive and the average Joe will most likely never get his hands on them.
I personally played a lot of NL throughout the years because i had an amazing account with like 8 fully geared characters with sick gear and decked out with charms. I even had 1 self found 40 life pb sk (so proud of that, still...lol). But if i didn't have that account, i'd probably play more ladder. I used to refresh that account every once in a while so it won't get deleted but i kinda forgot at some point so i lost everything.
Ladder is a lot more fun to start fresh either with friends or strangers from random communities. There are some communities that are still active like d2jsp or Slash-Diablo but they usually tend to be a lot more active around ladder resets. Slash-Diablo has its own server i.e it does not run on b.net live and it supports certain mods including the resolution mod afaik. There were some issues with the latest version a while ago but i don't know if they fixed that yet or not.
The spam is still rampant and annoying. the best way to avoid spam is to create games with a password. Even if you start a random game and some random guy joins to play with you, offer him to join you in a new game with a password so you can avoid the constant spam bombardment. If you played it a year ago then not much have changed since then.
Today, i think that the most fun ways to play D2 are when you limit yourself in a certain way. Kind of like all of those iron-man challenges that people used to run. Like, playing a game where you try to finish Hell without using runewords or using only rares or whatever. Trying to go for weird builds like a sword-weilding amazon or a singer barb. If you don't mind single player, then it's far superior to b.net imo because of the smoothness of the gameplay, never suffering from bad latency or "realm down" crap if you create and leave too many games, too fast.
A really fun (but expensive) build to run is the GF barb. Gold find barbs are so hard to gear for but are so damn awesome and rewarding... Something like this https://www.youtube.com/watch?v=LGko9SFzTww - but for some reason this dude is not using leap to knockback the mobs. Anyway, D2 is full of weird and awesome stuff.
A run with no additional completion requirements; anything goes. The "default" category for speedrunning a game. The term comes from the old school Metroid speedrunning community. Metroid has a percentage counter, while other games may not, but the term stuck around.