The point of Nadal being epic is his amazing defensive shotmaking coupled with his ridiculous consistency off the ground which means lower ranked players usually try to go for the tactic of taking a racquet out of his hands. When they're feeling it, it makes for some spectacular matches (like Nadal-Verdasco, offensive vs defensive baseline tennis at its peak). Fed and Novak (to a lesser degree) by comparison dictate and rush players so they don't really have time to setup their shots, it's a different approach to the game, you'll often feel you have a shot to beat Nadal if you just execute near flawless aggressive tennis for a prolonged period.
Also, Nadal does have the most on-court intensity I've seen since Hewitt. Whether one likes it or not, he can make a tennis match feel like boxing. I think it's a big part of his appeal.
Not my cup of tea overall but I appreciate his presence in the game.