If they buffed his stun to 25% chance, it would make him very playable.
Insanitarious makes his damage go through the roof very early, as well as increases his HP by a lot. When you get your shrunken you are able to disable one of their heroes very easily for at least 5 seconds, while dealing a decent amount of damage to him. Charge with magic immune (12 second+ charge) is a very way to initiate.
Stampede should also provide a haste equal to 1/2 of his current speed increase to nearby allies. This would allow for a massive rush of creeps and heros following rampage into the fight.
Right now, he is nothing more than a pubstomp hero, but with these changes I feel he could become competitive as an initiator/disabler.
Rampage is a hero that ramboes into 1v5 and gets a kill then dies. Then he rages at his teammates for not supporting him or bragging that he got a kill but they didn't.
He's KDA is usually 5/10/0. 5 kills and 10 deaths because 50% he will get a kill and die and if he doesn't get a kill he still dies. 0 assists because he is always the first one to go in, first one to kill, first one to die, and since he only attacks 1 hero, he'll kill that hero and die and not get any more assists.
Rampage is a great hero to solo kill a farming carry but against any decent teamwork, he really shows off he's 'Worst Hero in the Game' reputation.
Indulge yourself while playing HoN with epic background music from The Legend of Zelda: Twilight Princess: