I'm still useing 3.0
So lets go there instead.
Shouldn't make much difference.
Slam attack d8 (not sure how this is as good or better than a martial weapon, most of this size category are doing d10 or more.
It's not the d8 that's impressive. It's the extra damage you get for having a STR of 30+ that's impressive. 1d8 plus a metric buttload of STR bonus is substantially better than a 2d6 greatsword. The fact that you can't be disarmed is just a nice perk.
DR 5/+1 (nice, but worthless at this level)
It'll be interesting to see how they update that DR to 3.5E. Yes, in 3E it's mostly a worthless DR by the time you're high in level, although I always found it useful when getting hit by archers; those that didn't enchant their arrows had a hard time punching through even light DR (and we had house-ruled GMW, of course).
menu B ability or two from menu A (random combat boost or noncombat aspect)
You can't underestimate these abilities. Menu A includes 60' flight, and menu B includes things like +4 Deflection AC. The biggest plus is the flexibility.
Need to know at least 2 different powers, this one plus an astral construct, if you want your construct form to improve this cost grows as levels increase. (definately NOT 'no cost')
And if you want to cast Tenser's more than a few times, you need two spells, an item creation Feat, a lab to make stuff in, money, and XP.
You can't count the Astral Construct power as a cost, because it's a legitimate power in its own right. If you have a player who uses ACs as his form of attack, it only costs him one known power to add this to his repertoire, which is exactly the same as a Sorcerer adding Tenser's.
So, item for item, Tenser's is comparable to your power used to make an AC4 shell, ASSUMING you don't allow the encapsulated psion to manifest new powers while inside.
psionic personal buffs are supposed to be stronger than the arcane equivalent. (there are lots of examples of that in the power section).
I disagree. IMO, it's not even close. Which powers were you thinking of?
Psions have quite a few good ones, but their biggest advantage is the lack of components (especially Material ones), which turns some good spells like Stoneskin and Forcecage into great powers like Inertial Barrier or Mass Cocoon.
But, there's no Mage Armor or Shield; the closest analog, Ectoplasmic Armor, is high level and has other limitations. And, Wizards get Mirror Image, Blur, Blink, Alter Self, and of course Haste. Psions get the Vigor and Biofeedback lines instead.
Or, they take spells like the Endurance/Bull's Strength/etc. line and combine them into one power, Animal Affinity, but make it self-only to balance. (Same goes for Darkvision/Vigilance for Psiwarriors).
Then there's the claw/bite powers. They're great, right up until you start needing magical weapons; at that point, only Claws of the Vampire is worth much.
Not stronger, just different. If anything, the Wizard can self-buff himself FAR beyond the Psion.
Also, I already accounted for the size difference problem, the power states that the construct needs to be at least the same size as the manifestor.
You're right, I missed that.
Now, you lose the use of basically all your equipment. Magic armor and weapons and other such objects you had as a character are gone, while the mage with his transformation gets to keep useing his.
A mage using Tenser's loses the effects of his Amulet of Natural Armor because the spell doesn't stack (until 3.5E...). He keeps his Cloak of Resistance, but the guy inside the construct can ignore two out of three saves to begin with (the construct's immune to most Will and Fort saves) as written.
The guy in the construct still gets the half the benefits of his Gloves of Dexterity and Belt of Strength. That may not seem like much, but it doesn't matter how big the belt is, 25+(STR/2) is better than (STR+5). Unless you can get to STR 40, that is.
Any weapon the wizard is carrying will be inferior to the slam attack the construct gets, not to mention its grappling abilities (and the construct can take Improved Grab!). And, the Wizard isn't going to carry around a Greatsword that he can't use 99% of the time for those few occasions when he casts this spell, so the weapon he uses will probably be a dinky dagger.
Headbands of Intellect, Cloaks of Charisma, etc. aren't useful to either person since they can't cast spells. Ditto for any item that improves spellcasting ability or casts a spell X times per day.
So, it comes down to the amount of armor a Wizard wears, or miscellaneous AC items like Rings of Protection. Almost every Wizard I know gets his armor AC from either Mage Armor or Bracers. A Psion might wear more physical armor, but they also have things like Ectoplasmic Armor.
There are also a few questionable ones. If the psion is wearing an item that gives Darkvision, does that transfer? Why wouldn't a headband of intellect still function fully if his mind replaces that of the construct?
Of course it is also your mind controlling it, so something that takes over your mind would still effect you.
Then you need to say that. As you wrote it, if your body is inside the construct it's untargettable, and "sharing its senses" doesn't mean the same thing as "single mind". Constructs have WIS and CHA for a reason. That'd be step one, then; say that your mind REPLACES that of the construct, so it has no WIS or CHA of its own (and Will saves, too) and becomes vulnerable to mind-effecting spells or things that affect Humanoids.
Also, constructs are inherently neutral (unlike a Wizard's summoned creatures), so if you don't change this, a "psion in a box" can arguably pass through Protection From Good spells... bad idea.
Since it goes away when the extra hp are lost, plus all of the other drawbacks, at this point I'm not even sure if the power is strong enough (let alone too strong). Turns you into the combat machine that after one round of hits all of your power goes away.
How many rounds do you see most Wizards keep Tenser's going? Tenser's keeps you from casting spells, so most times I've ever seen it used (which isn't many) revolved around a specific situation where the Wizard KNEW his spells wouldn't be useful. But, if there were a situation where you wanted to Tenser's but still needed to occasionally cast spells, you wouldn't keep it on for the full duration.
The fact that it wears off after a couple rounds of combat hurts a bit, but unlike Tenser's it has non-combat applications (flight, for one) and for constructs 27 HP can last an awfully long time. They're immune to a lot, and can pick resistances up pretty easily. Or, if I just want it to last longer, I'll take the menu B choice that gives 3d10 temporary HP; now I can take 44 damage before my cocoon goes splat (or better yet, 43 damage and then one huge 200-point attack that finishes it off).
Then, there's the fact that it's "just 27 HP". Let's say I'm a 12th-level Psion who specializes in INT, or else I wouldn't be casting this, so I'd have 4+11d4+(12*CON bonus) HP. With CON 14, that's 55 HP, so even without the 3d10 extra I'm giving myself 50% more HP than I had before. With it, I'm nearly doubling my effective HP, and that's assuming there wasn't any wasted damage, sneak attacks, or criticals that the shell absorbed.
One problem is how it's phrased. If your body is in stasis inside the shell, you're just utterly invulnerable to a LOT of things. Critical hits, energy drain, ability drain, sneak attacks, all those Fort save things. Anything that targets creature type "humanoid", because they can't target me directly. If someone Disintegrates me, it destroys the construct but I, the Psion, am fine. Can an incorporeal creature reach through the construct to attack me? If not, then there are a few more creatures that would be totally ineffective against me.
Also, realize that Astral Constructs scale awfully quickly. An AC4 might be approximately as good as a spell like Tenser's, but what about the 9th-level version that uses an AC7? Much, much better. Then, there's all the Feats. Extended Construction increases duration to 1 minute per level. Advanced Construction adds a whole slew of new options to the menus, including Fast Healing and more HP. Then there's the one that lets you choose more menu abilities for each construct.
Frankly, I think you'd be better off just making a generic buffing spell along the lines of Tenser's. Give a little DR, Natural AC, STR, DEX, and maybe one minor ability from menu A, and you no longer have to worry about things like construct traits.