Hobbies And Interests
Pro: Minions
One of the biggest benefits a Death Knight brings to PVP is his minions. Death Knights have the ability to summon ghouls to assist them in combat with the spells "Raise Dead" and "Army of the Dead." These spells each summon one and several ghouls respectively, creating additional opponents for enemy teams to deal with for a short time. Unholy Death Knights have their "Raise Dead" minion out permanently, and gain an additional spell called "Summon Gargoyle" that enables them to summon an additional gargoyle minion with unique abilities. A Death Knight with upwards of 10 minions fighting by his side can be a fearsome opponent and a valuable ally.
Con: Complicated Playstyle
Death Knights have a unique resource system, Runic Power. Each Death Knight has six runes: two Blood, two Frost, and two Unholy. The exception is Frost Death Knights, who replace their Blood runes with Death runes. Most moves cost a rune that corresponds to its type; for example, "Plague Strike" costs an Unholy rune. Death runes can be used with any rune-dependent spell. Using these moves generates Runic Power, which can be used for other moves like "Frost Strike" or "Death Coil." Different moves and talents can renew runes, which otherwise have a cool-down period before they are available again. Some moves can also recharge a rune as a Death rune. While this system itself is not a hindrance, it can be complicated and requires time and practice to master.
Pro: Versatility
One of the benefits of playing a Death Knight in PVP is that each specialization brings a unique benefit to the field. Blood Death Knights, as a tank specialization, are extremely durable and have many self-healing abilities as well as damage absorption and avoidance capabilities. Unholy Death Knights have more powerful minions and provide good sustained damage for lengthy fights. Frost Death Knights are useful for dealing sudden bursts of damage, and can be useful in a sustained single-target fight with a two-handed weapon or cleaving through crowds while dual-wielding. This gives the Death Knight several angles to play from, making it more likely that you'll find a specialization and play style you enjoy.
Con: Silence
Unlike most of the other melee classes, the Death Knight is particularly susceptible to silencing. In contrast to the moves of Warriors, Rogues, Feral or Guardian Druids and Monks, Death Knight moves technically count as spell and draw from damage schools other than physical. As such, an interrupt spell like the Rogue's "Kick" can render a large portion of the Death Knight's moves unavailable, leaving her with only auto-attack damage to rely on. A well-organized team carefully timing interrupts can easily dominate Death Knights, making this a serious vulnerability in a class that will by necessity be in interrupt range at almost all times.
Pro: Defensive Cooldowns
The Death Knight has an impressive array of defensive cooldowns that make them harder to knock down than some other classes. These chiefly come in the form of "Icebound Fortitude," which reduces all damage taken by 50 percent and "Anti-Magic Shell," which reduces all magic damage taken by 75 percent until you've lost 50 percent of your maximum health as damage. As a tank class, Blood Death Knights have a couple of extra cooldowns to keep themselves healthy, namely "Dancing Rune Weapon," which grants a 20 percent increase to parry chance and "Bone Shield," which reduces all damage taken by 20 percent and remains active until you've received six damaging attacks. "Army of the Dead" is also augmented for Blood Death Knights, granting damage reduction equal to the sum of your dodge and parry chances -- if both dodge and parry are 15 percent, you'll gain a 30 percent damage reduction buff. Blood Death Knights also get physical absorption shields when they heal using "Death Strike," thanks to their mastery skill, "Mastery: Blood Shield."
Con: Regular Defenses
When not using defensive cooldowns, Frost and Unholy Death Knights aren't the hardiest melee fighters. While they are a plate class like Warriors and Paladins, these two specializations suffer from decreased self-healing capabilities and less damage mitigation than Blood Death Knights. This makes them "squishy," an in-game slang term referring to their inability to withstand sustained punishment.
Considerations
Like any class in both PVP and PVE, Death Knights can shine with an experienced player and a balanced team. The Death Knight can be a complex class requiring time, practice and patience to master. In some PVP situations, they can be extremely useful -- for example, when doing a Warsong Gulch battleground, the Death Knight's "Death Grip" can easily drag a runaway flag-bearer back to his demise. As the game continues to evolve with new patches and expansions, the Death Knight class will continually change and be rebalanced.