It's OK. Top few for 1v1s, forced dots+tankiness and cc because up close. 1v1 means easy and annoying permablock.
Doable in groups, but every class bar stamDK has better utility. (sorcerer has talons and petrify, warden has effectively talons, other classes have better damage) Works well for BGs where you are in a smaller area and have more control over the game.
Awful in openworld solo. By far the worst mobility, only survival method is block turtling since wings is very limited, which in turn lowers burst damage. (Effective burst can be really high in light, arguably nb tier.)
Bad sustain too, on account of relying s/b in most cases, and battle roar providing less sustain than all class based methods. Little defence against ranged builds anymore discounting wings. (bugged, low limit, high cost)
I think it’s good and fun to play. The only mag class I think is worse than dk is Templar for solo pvp so if you want the best class I would do sorc nb or warden
People talk a lot of smack about how bad magDK is nowdays but I do ok with mine in Cyro. Mobility has always been an issue, but we have a lot of CC to keep the enemy locked down. Thats my favorite part about a DK is you CONTROL them. You petrify, talons, stone giant, etc are all very effective at keeping the enemy under your control while those dots tick tick tick. Survivability is good (i wear heavy, the only choice), and resources are managed through pots and ulti. Leap is a beast that gives you back a ton of resources and provides mobility/execute. If built right, your dots should apply heavy pressure while you keep up the CC/whip, proc the BSW, watch for the skoria and them hit them with the leap. Ranged builds are challenging if they are fast or can escape easy like cloak but stone giant takes care of that issue. LOS is your friend in a lot of cases. I run SnB both bars but if I'm feeling frisky I'll run DW front bar.
I think the magDK is a challenging class to play right, but easy to understand and get the hang of. I dont feel we are in the same spot we were in Homestead, but I think a lot of people are blowing things out of proportion in terms of how bad the class is.