I am currently reading my way through a long list of science fiction and fantasy titles. (http://www.npr.org/2011/08/07/138938145/science-fiction-and-fantasy-finalists if you are interested in the list).
Time Enough for Love follows Lazarus Long through a vast and magnificent timescape of centuries and worlds. Heinlein's longest and most ambitious work, it is the story of a man so in love with Life that he refused to stop living it.
I know that a lot of people love Heinlein and I have enjoyed a number of his novels too. This one, however, suffered from the need of editing--it was much too long and repetitious, especially if you have already read Stranger in a Strange Land or Friday. These books make me wonder what kind of person RAH was and what it would have been like for his wife to live with him.
He is a great proponent of being self-reliant--but the farther we get from the horse and plough, the more reliant we become on others to build our devices, be they mobile phones, computers or spaceships. We live in a society where we have to rely on others--I don't know how to make cloth or even how to turn cloth into clothes. Someone else does my farming, gardening and butchering and it will be that way until the replicators show up (and even then I'll be reliant on the replicator repairman!)
RAH also seems to have some odd ideas about what women want (here's a clue, we don't necessarily want umpteen babies!). It seems like Lazarus Long always has some woman hanging onto his leg, begging to be impregnated. That got really old for me after the first time, let alone after the 20th time! Research has proven that when women get educated and have access to birth control, birth rates go down. We prefer to have fewer children and to invest more in those children, rather than produce dozens, and I'm sure women of the future, no matter how long they live, will continue to feel that way.
Basically, I was irritated with the women characters for the duration of the book--they are not like any women that I know. In the end, I think they say much more about Heinlein that they do about humanity or our future.