At any rate heres my idea for a charm...and you would have to uber for this charm..yes get keys make doorways then get 3 organs from those doorways to make a portal to the uber against belial azmodan and diablo. A real uber!!! Not that sissy one against mini bosses. Whats really important here is a set Monster Power. Either you can do it or you can't.
Another very important factor is that you can trade all the stuff involved in this because thats what makes it have good replay value. Not that the hellfire ring was a bad idea (except the name - anyone remember the hellfire torch from d2?) but it is fun to have something (not plural) to show off and cant get any other way than doing it yourself. But don't limit item availablity for trade...expand it!!! Allow people to be able to get great items by only paying an arm...not and arm and a leg. Now a great item would be a perfect roll on the first torch below (or a ring/ammy with ar - main stat - (vit-or-ias) - crit chance - crit damage)
Shard of the Crystal Arch (or something CREATIVE like that)
+(10-20)% damage (perhaps 10-15%? idk let us have some fun and if its op add another 5 levels of mp or something)
+(75-125) all res
You could also have small charms - like d2
Small Charm of Focus
5-10% reduction in cooldown times
Small Charm of Damage
Small Charm of Res All (or a specific res)
+(25-35) all res
+(45-60) a certain res
or you could have fire or ice or physical damage like they already have.
Something very important too...in order to keep a balance you must carry these charms in your inventory. Its the trade off of slowing you down while looting in order to be more powerful.
The bottom line is that the item stats vary too much and in order to balance it out charms would be a good start. Being slight overpowered on a toon with 300 hours and without falling into an over powered build is resonable. And im not talking about blowing through mp0 and even mp5. Im talking above mp8. Yes that is about as endgame as it gets I suppose but I would have to play for hundreds of more hours to get to mp10 and move through it at a reasonable pace. For some reason it just irks me that I can't have the same chance at items as someone who has put 1000 hours into the game. Its not right to punish someone because they haven't played your game as much as others.
for an example on how items vary too much in D3.