Yes, I did. The beta (available from a website on one of the other posts, i think) is more or less the full-featured mod, except it uses the default Normandy campaign. As such, it includes Eldar, Dark Eldar, Tau, Imperial Guard (Cadians, Stormtroopers and Catachans), Space Marines, Civilians/PDF, and the marines from the Aliens movie. The Space Marines look about normal size, but they have a really high armor save, so it takes a lot of bullets to down them. They also have the best weaponry.
I can answer these, having played the beta:
1. As far as I can tell, the only psychic units are the eldar farseer and seer council, and the IG "mindpriests" (probably sanctioned psykers). They all have a "weapon" with unlimited ammo that works invisibly and incredibly well at mid-close range.
2. The weapons act more or less like their CC5 equivalents. If anything, they are weaker due to the personal armor system that reduces actual deadliness.
3. Having only played the IG in the game, I can't say, but from what I have seen, they are pretty fast and can tear you right up in close combat.
Edit: Also, is this ever going to be released, or what? It's been weeks.
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