Grey Knights in 6th Edition

Lets look at Grey Knights in 6th edition. First of all, keep in mind that I play pure Grey Knights. That is no Inquisitor's or Inquisitorial Henchmen which are so popular in tournaments. Lets look at what is good for Grey Knights:

The Good:

1. Grey Knights are an 'Elite' army in that they individually cost a lot of points, but their points cost compared to an equivalent unit in another codex are actually comparable or cheap. For example every single Grey Knight has a Force Weapon and a Storm Bolter. Even if you don't activate it, the Nemesis Force Weapon counts as an unusual force weapon (Str as user, AP 3). For example, a Grey Knight Purifier (from the Elite Slot) costs 24 points per model. A Wolf Guard (also an elite slot) comparably armed with a Storm Bolter and Power Weapon would be 31!!. You will probably be outnumbered, but model for model, other armies cant compare to Grey Knights.
2. Grey Knights look like an assault army, but they are actually a shooty army with assault elements. What do I mean by that? Well for starters every model in the army is getting at least 2 shots at 24" (unless you take Incinerators). You can also upgrade the basic shooting of the army to be Str 5 with psybolts. In addition, you can get 1-2 Psycannon's per squad depending on what you take. Psycannon's are probably the best ranged weapon in the game in my opinion. 2-4 Str 7 Rending shots at 24". These are souped up Assault Cannons and they destroy men and vehicles alike. Grey Knights should always pour as much fire as possible in to a single target and then follow up with a devastating assault. They are dangerous enough in the assault that most armies will not want to charge you so you stand a good chance of getting the charge off, and if they do charge you, overwatching with 8 storm bolters (16 shots) and 2 Psycannon (8 shots) almost guarantees hits that can whittle down the opponent before they get to swing back. If you throw in some special grenades as well it should be a victory for the Grey Knights. Opponents that expect you to focus on the assault will be in for a shock when you shoot them off the table through volume of fire.
3. Psychic Powers: The entire army is psychic and has some cool tricks up their sleeves. Individual squads have group psychic powers like Hammerhand which gives a +1 strength or Astral Aim which lets the Devestator  equivalent shoot and ignore line of sight restrictions. In addition, Grey Knights have access to Mastery level 3 Librarians and the codex powers are almost all worth taking. On top of that they have access to the Divination school from the Basic Rulebook (BRB). With Divination you can give a squad a 4+ invulnerable save, or let them reroll misses in shooting and close combat. Its like twin linking all your shooting and master crafting every attack dice!
4. Paladins: The toughest, baddest Grey Knights may eventually become Paladins, two wound Terminators with easy access to Feel no Pain. these guys also become scoring if you take one of the special characters. A lot of tournament lists evolved around the use of these guys so I wont go in to them too much here.

The Bad:

1. Grey Knights rely more on psychic powers than other armies, this can be a hindrance if your opponent has a way to shut down your psykers, like Eldar Runes of Warding, or Space Wolves Rune Priests.
2. 24" Range - Grey Knights fight heavily at the 24"-30" Range. A mobile opponent can take advtange of this. There are ways to overcomes this (Interceptors have an effective 36" range with their Jump Packs + 24" Shooting) but true long range firepower, like Lascannon's, come from Vehicles or Dreadnoughts and those are expensive and/or fighting for slots better spent on other things.
3. Grey Knights can struggle with AV14 vehicles. There are not a lot of options in the Codex for pure Grey Knights to take anti tank weaponry, and all of them are based on Vehichle or Dreadnought chassis.

The Ugly: (How 6th changed things)

1. In 6th edition, weapons in close combat have AP values now. All of the Nemesis Force Weapons except the Daemon Hammer are AP3. This means that Grey Knights have a hard time dealing with 2+ armor saves in close combat. If they are unable to shoot 2+ armor off the table through volume of fire they will have a hard time getting a scoring 2+ squad like Deathwing Terminators off an objective.
2. In 5th, Grey Knights were awesome because you could outshoot almost everything at the 12 to 24 range due to all the weapons being Assault 2. In 6th edition, rapid fire weapons can now shoot once up to 24" (twice up to 12") even if they moved, which has lessened the fire superiority that Grey Knights enjoyed in 5th
3. Psychic Powers/Defense: The best powers in 6th edition are those that buff your own models. This is because with a few notable exceptions, you can not do anything to interfere with enemy powers that target their own guys. While this does help Grey Knights, it is more of a hindrance than a help because letting a squad of Plasma Cannon Devastators or Long Fangs ignore covers and reroll misses will screw you up more than any offensive power ever will.