1) He was one of the most complete HW at that time, and even in todays standards : Great striking, great judo/grappling, great subs. Beat Cro Cop and Nogueira at their game. He had great hips, quicks hands for his size, and he was also explosive. That's why Cormier was called black Fedor, cause he reminded us a lot of him. Pretty flattering comparison.
2) He was entertaining. His plan was to completely kill you with his bare hands. No time for tactical breaks during the fight. He was there to bring it all even against Cro cop he was at the center of the ring chasing him like a terminator. He gave us fantastic fights (Rogers, Arlovski, Fujita, Randleman, Cro Cop, Big Nog) to remember.
3) He was not big for a HW. He did not rely on any physical attribute. He was a fleshy 6 ft man who had to rely on his aggressiveness to compensate for the rest. I mean look at the size of his brother compared to his.
Bonus : The fact that he did not care for any trash talk games and antics make him even more likable.
WAR FEDOR