Well, now, there's room for debate here.
The description of the Ring makes no mention of targetted spells.
It affects spells "cast upon" the wearer.
What determines whether a spell is cast upon him?
Hold Person: single target, the wearer. Pretty obviously yes.
Inflict Light Wounds: single target, the wearer - range Touch. Spell Turning wouldn't work... does a Ring of Counterspells?
Bane: multiple targets, including the wearer. It's "cast upon" him... but also on a bunch of other people. Is it countered? For everyone, or just the wearer?
Ray of Frost: Effect: ray. If it's aimed at the wearer, is it considered to be cast upon him?
Fireball: Area. If it catches the wearer in the spread, is it cast upon him?
If the ring used the phrase "spells targetted on the wearer", it would be far more clear. But "cast upon" is not a clearly defined phrase.
-Hyp.