Incantations are spells that can be cast by anyone, regardless of class, level, or caster abilities. They are often time consuming rituals that take multiple people to accomplish and a string of successful skill checks with really high DCs.
I have a player in my campaign that is hot to try them out. I dunno, though. They strike me as a lot like the epic magic from Epic Handbook. Some people like epic magic, but I'm not one of them.
One point in the favor of Incantations, though: Because of the stringent requirement that can be added to them, I think they would fit great into CoC, representing ancient magic of the type best left alone.
Other than that bit of flavor, I think it has a lot of potential abuse - no limitations on casting per day, for one.