The heroic figures of The Lord of the Rings are Aragorn and Frodo. One is a greater man, noble and powerful, who fights epic battles and the second is a childlike hobbit wondering why he was chosen to destroy a "wicked" ring, a question which will increase his burden on his shoulders until he will pass through all sorts of dark experiences, eventually reaching the level of a "magic hero".
On the other hand, The Hobbit is the story of Bilbo Baggings, who was again chosen to take part in an adventure, the pursuit of happiness (because all that glitters is gold). I don't see it as a prelude for the famous trilogy, even if the ring is mentioned here and there. It's power is not so well emphasized. All that we know is that it makes you invisible and made Gollum run astray.
This book is a simple "bildungsroman" type of novel and when everything is done the life gets back to normal. Of course you can feel that there must be a sequel to such an enjoyable book, but the trilogy really stands alone. It's very complex and it all happens around the ring, it goes in circles and drives you mad until you reach the bottom of it and redeem yourself along with Frodo.
