Long post, because I like to go in-depth on debuts.
We can finally see a preview of the battlemind, a Con-based psionic defender. They remind of psychic warriors: you get to tour around in heavy armor (up to scale), use shields, and get a nice spread of weapons. Is the name better or worse? Eh…thats up to you. I personally didnt mind it much when they used the name in D20 Modern. Naming conventions aside, this class looks fucking awesome. I think that it will do very nicely in letting me play something close to a fury-crafting knight from the Codex Alera series…
Like psions, they get power points and can burn them to crank it up to 11 when they feel the need to. This means that what would normally be their encounter disciplines are weaker than usual, and hit that “balanced-or-better” mark only a set number of times per encounter depending on how you manage your power points. This adds a layer to resource management in a way that doesnt drastically add to bookkeeping or changing the way powers work at the core. I much prefer this to learning numerous subsystems, as in the past.
I mentioned their mark mechanic in a previous post, but I’ll explain it again. They have three at-wills that come into the equation. First, you use battlemind’s demand to mark anything within 3 squares as a minor action, and it lasts until the end of the encounter or you use it again (basically how swordmages do it).
Now, if a marked enemy tries to shift to get away, you can use blurred step to shift after them. So, unless they can shift at least 2 squares its not going to do much good.
Finally, if the enemy attacks an enemy and you’re within melee range you can trigger mind spike as an immediate reaction that deals automatic damage equal to the amount your ally took. Just to make things clear: there is no roll on this. You deal this damage no matter what. The enemy just has to be within melee range.
The battlemind class feature that determines your “style” is Psionic Study, but the only one in the debut is Speed of Thought (Battle Resilience will be included in Player’s Handbook 3). Speed of Thought grants you the speed of thought (surprised?) encounter discipline. It lets you move for free whenever you roll initiative. Its quite a distance, and you can even do this during a surprise round. For a defender this is insanely awesome.
Battlemind disciplines are keyed to Constitution and depending on what class feature you took, you can get some more out of Wisdom or Charisma (Wis for Battlefield Resilience and Cha for Speed of Thought). As the article only features the Speed of Thought class feature, if you are going for optimization then ramp up Con and Cha to get the most out of it (hobgoblins and half-elves ftw!).
There are waaay too many disciplines to go into, so I’ll just go over the basics, by which I mean the level 1 stuff.
Demon dance deals psychic damage and imposes a penalty to opportunity attacks. You can augment it to also negate threatening reach, as well as boost the damage and completely negate the ability to make opportunity attacks, period.
Twisted eye damages a target and imposes an attack penalty based on the number of allies nearby. You can augment it to have it fire as an opportunity attack or cause it to just fucking blind the target for a turn.
Whirling defense damages a target and lets you mark them. You can augment it to grant bonus damage to mind spike, or target every enemy around you. Bad ass.
Daily disciplines dont get augments. They just do what dailies tend to do, which is to say that they do something on a hit or miss (if they even require attacks at all). Battlemind daily attacks come in an even mix of the normal fare and stances. The stance attacks remind me of warden daily evocations because they open up a new at-will attack that you can use for the duration of the stance., each granting you the ability to make a special attack until the stance ends. They’re all opportunity action attacks, so really its just a way of giving you an alternative to using mind spike.
Allies to enemies deals double weapon damage and causes an enemy to attack an ally of your choice. Nothing too complicated, and depending on the monster it could be really awesome.
But…Steal unity strike, on the other hand, deals triple weapon damage in addition to allowing you to make opportunity attacks against marked targets that deal double damage on a hit. They’re also keyed to Constitution, so they are much more effective than normal.
The balancing factor is that you can only do these stance attacks as opportunity attacks against marked monsters that dont shift to get away from you. Otherwise you kind of have to stick with mind spike. I know a lot of players complain that their DMs never have monsters provoke attacks from the defenders (which is kind of the point), and if thats true these will end up being super awesome abilities that likely will never see application. Still, one can dream.
There are two paragon paths, steel ego and zephyr blade. Both are suited for the Speed of Thought build but play very much differently.
Steel egos can use mind spike more frequently on an action point, AoE it for automatic damage whenever, and regain power points on a crit. Their encounter attack lets them basically hit what the fuck ever they want with mind spike for a turn (and also making it usable as a free action once, so you could theoretically do it twice). I’m particularly fond of fear and loathing, which deals a lot of psychic damage and makes the target provoke opportunity attacks whenever it makes a melee attack (save ends). As an added bonus, you can slide it whenever it gets nailed by an opportunity attack.
Zephyr blades are fast mother fuckers. You add your Cha mod to attacks against targets suffering from a few conditions, and gain a passive bonus to Speed. A few of the powers grant you insubstantial and phasing, which adds to your mobility options. Knifing wind isnt terribly interesting, dealing damage with a daze kicker (you can augment for more damage). Storm dance strike, however, is a stance attack that lets you attack up to two creatures and teleport at some point. The granted opportunity attack slows the target and lets you both teleport away. Excellent for positioning!
Now, there are only five feats, and the shitter here is that two are Heroic, two are Paragon, and one is Epic. Not a lot of variety. 
This in the addition to a lack of supporting magic items is my main dislike for actually playing debut classes. I dont mind giving them a shot in one-shots and delves, but in actually long-term play? Fucking forget it. Not enough to maintain interest…but still cool to see whats up and get some ideas brewing.
This looks like it will be my class of choice from PH3 (with the monk right on its tail).
Awful Good Games 