I'd be interested to see DC's exact description of what a power ring does.

•  Is it just a force projector?
• Can it do anything?
• Is it intelligent?

Me, I think the ring should only be a powerful telekinetic device that allows you to create force bolts, provide telekinetic transportation and create temporary "solid energy" constructs. At the very least, all of its abilities should only have a temporary duration.
For example, it can make a cage to hold Evil Star in, but that cage shouldn't exist for ever. However, it could bend and mold regular matter into a cage that would be more or less permanent.
In my opinion the power ring shouldn't be an energy force (except for "paddle boat"-like engines). It shouldn't be able to rearrange molecules unless the wielder actually understands the molecular workings. Nor should it create dimensional wormholes.
You can use telekinesis for a lot of things, but you have to know how to use it right, otherwise you end up with a jumbled mess.
The ring shouldn't just magically fill in the knowledge gaps of the user.
If the ring can in fact do anything, then why even have a Green Lantern? The guardians could just sit on Oa and blast people from afar.
If the ring is intelligent (an implication that has been made when G'nort used one), then I ask again, why even entrust it with a Green Lantern. Just have it float through space, righting wrongs.