There's been a lot of questions/discussions/complaints regarding DK DPS in Fury . Some say it's too hard. Some say it's too boring. Some say it's too weak. Some say it's just fine as is for the most part. I fall into the latter category; my own experiences as a DK tank and DPS'er have shown me that the class is perfectly competent and capable of doing competitive DPS...
There is a maximum DK DPS guide for you in fury gold .if you are interested in it .just look through. I believe you will learn something from it.
With that said, the DK is a very complicated class to begin to master. There are several mechanics at work that make this class so.
1) It is a melee class. Generally speaking, it is more dangerous and harder on positioning for melee classes than for ranged classes. There are certainly some exceptions to this, but one cannot deny that there are more melee unfriendly fights than there are ranged unfriendly fights in fury gold game .
2) The class runs on two resource systems as opposed to one. Runic power's (RP) closest equivalent is rage, but even that is a limited comparison (RP is only generated from using rune moves, and does not generate from being hit or hitting something with auto-attacks).
The rune system is somewhat similar to energy, except it is much more stringent and restrictive in terms of what you can use runes for (Death runes help to mitigate this a bit) and there are extremely few ways to refresh runes before their 10 second cooldown. This can be very attention-demanding for some players, especially also given the need to watch for melee dangers/repositioning.
3) The class also makes usage of a DoT's. For shadow priests and affliction warlocks before 3.0, the rule of thumb for DoT's was to let them run their full course, then immediately refresh after they had worn off (This is so that they can get their last tick of damage, and to maximize the amount of time you spend not refreshing DoT's so you can use your other damage-dealing moves in fury gold).