Well I did on X-COM: EU, though I did end up losing for that reason I suppose, near the end of the game. I blame them for that though, it wasn't until you actually tried to attempt an attack on the alien mothership that it told you of this arbitrary requirement which could have been mentioned 10 hours (game time) prior. Perhaps that's how the X-Com games work though, and if that is the case I guess I'm just a glutton for punishment.
The Firaxis XCom is a very different game. It's inspired by the original comparing them very much doesn't do either any favors really. Best enjoyed separately
Though when I played the firaxis one I think it did tell me about the psionicist requirement, or at least that I wanted to train one up. I did anyway because psionics were largely what let me turn the tide in the original (though there was no hard rule requiring it).
In the original you still got bitten hard by things you didn't know, but they were things that it made sense that you didn't know them. Thus far that's also my experience with xenonauts. Like:
ZAP! (My sergeant whacks new enemy with stun rod, because I want to take one alive)
... and it doesn't fall, despite my being able to one-shot their massive overgrown lizard shock troops with one, and this hit doing about as much stun damage as the other one took to down
ZAP! (My sergeant whacks it again, big numbers, alien still standing)
(Alien shoots my sergeant in the face repeatedly, but between the difficulty causing misses and my sergeant's armor he barely survives to next turn)
ZAP!
ZAP!
"I hit the freaking thing four times with a giant cattle prod, what gives!?"
(reload from slightly earlier save, and just gun the thing down rather than get my sergeant shot up)
Post-mission autopsy: it's an android.
*facepalm*