I would rule that only basic attacks and Power Attacks are allowed. That seems to best fit the spirit of the spell. I would allow two-handed damage, but would probably impose the restriction that the spell then becomes a full-round action (not one full round, where it takes effect just before your next turn; I mean like a full attack action or other action where you can't take a move action in the same round), to fit in with the rules for throwing larger weapons (PHB 113, Thrown Weapons). Don't forget to apply any non-proficiency penalty to the roll, too, since it does state "just as if you attacked with the weapon in melee."
However, I could see how a trip attack could also be appropriate: Hurl the weapon at ground level, with it spinning along it's path like a lawn mower blade, so that it strikes at foot and knee level to trip; the problem comes in resolving a failed trip attack. I would treat it as using a whip, where you can drop your weapon to avoid being tripped, and end the spell with the weapon in the square where it was when it failed the trip attempt, and not have it return to you?. Disarming could also work, but if you fail the disarm, the spell ends again and drops the weapon where it failed the disarm attempt at, or it could be grabbed if the target of the disarm had a free hand.
But all that may be too many options for a second-level spell. I personally would keep it as standard attacks and power attacks. And as a clarification, if you cast this spell during a suprise round or other time when the enemy is flatfooted, you would apply sneak attack damage as well, as I read it.