LogFAQs > #986062515

the primary thing it does is ties his essence to middle earth, which gives him dominion over it and makes him immortal. all the other rings impart control of the world to the bearers in relation to their own personal power and ability, its why rivendell and lothlorien are untouched by time and why the dwarven ring holders gained massive amounts of wealth while they held them. the one ring does the same thing but greater, because you're talking about a ring crafted by a god, and also acts as a way to control the other races who have been 'infected' by the lesser rings.

even with the ring destroyed he's still tied to middle earth, its just that he imparted so much of his 'soul' into the ring that its destruction left him so dispersed that he cant really do anything. i think tolkien called his state little more then a shadow after the ring was gone.