Pretty much what foxhound said. Early UFC differs greatly from modern UFC, both in terms of athletes and rules. Originally, there were no weight class distinctions, no gloves, fighters were allowed to wear various articles of clothing (like a GI for example), and pretty much all fighting tactics were permissible (including hitting the back of the head, kneeing a grounded opponent, and even groin shots).
What resulted from this was basically watching two "red-necks", often overweight and out-of-shape, swinging wildly at one another until one either was knocked out or they were both gassed out. Then the Gracie family comes along, and utilizes the UFC in showcasing their style of Brazilian Jiu-Jitsu. Suddenly you get more well-rounded fighters, and actual athletes who make their living training daily and competing. You see guys like Ken Shamrock in UFC 3, and it all goes uphill from there.
In short, modern UFC is worlds better than past UFC, and is pretty all-around phenomenal. And no, I'm not a paid representative of UFC....just a huge fan, lol.