Extremely good but with a narrow peak. He came into Pride super green and was controlled and subbed by Sakuraba. Sakuraba is a legendary fighter but one who lost a lot of bouts because he was a pudgy middleweight who took way too many fights against super juiced up 205ers. In Rampage’s final form he would have crushed Saku, but he entered Pride as essentially a wrestler only.
He quickly improved and once he hit his stride, he only lost to Wanderlei Silva and Shogun in Pride and in competitive bouts.
By the time he came to the UFC, he not only had power and wrestling, but his hands were amazing. Top tier for MMA and especially dangerous because he was a really good wrestler too both offensively and defensively.
He quickly got the LHW title by one-punching UFC legend Chuck Liddell. Chuck up until that point had walked through easy powerful strikes to the chin, but one hook from Rampage and he was sleeping.
From there though it was a slow decline for Rampage. He beat another (undersized) legend in Dan Henderson to defend his title and then had some kind of drug-fueled incident where he ran his monster truck into a pregnant woman who lost her baby afterward.
He lost his belt too to Forrest Griffin of all people. Basically he couldn’t defend a low kick and got more and more stationary and less sharp with the hands. He still had quality wins after the loss to Forrest, but over the course of the next few years he went from probably the best 205er on the planet to just a pretty good fighter, and then eventually to someone who is fat and can still kick our asses but is nowhere near an elite fighter.