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.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.

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). Granted that the DoT's are not a tremendous portion of our DPS, but for those looking to maximize their DPS this is something you need to consider.

4) The class makes use of arguably the most instant-attacks in the whole game in order to do the majority of its DPS. Most of the time, your usage of cooldowns will be fairly simple decisions (I have my diseases up and a frost/unholy rune combo is available, so I will burn it out my Scourge Strike/Obliterate. I have blood runes up, so I will blood strike/heart strike). But there are many decisions you make on a micro-level that are small at the moment, but overtime these decisions will ultimately decide just how much extra output you are squeezing out through your skill priorities (Do I sneak in a death coil or use a blood strike? I'm sitting at 60 RP and I have a F/U move popping in 1 second, do I use a RP dump or wait and use the FU move?) This is a class where attention to detail makes a big difference, along with doing some mental math when monitoring your RP.

Perhaps there are more things to mention, but this is what I can think of at the moment. What I'm about to post is not for people who are just looking to play DK's in a very lackadaisical manner. These are things I have learned and experienced that I think may help you if you're looking to do your role as DK DPS'ers well, at least as far as my experiences with unholy and frost have been in raids.

Without further ado, let's get to the meat of what I hope will interest you. Please note this is primarily for the purposes of raiding and running instances, and not for PvP or solo-grinding.