I rented this a couple days ago. I played it for about 45 minutes and was not impressed at all. The Wii controls are not very responsive, and the only learning curve involved is the 20 minutes it takes to figure out what ass-backwards way you have to move the remote in order to get your character to actually do what you want--and even then it's a crapshoot.
For the $30 they're asking, you'd really be better off buying an N64 and Rampage World Tour.
If you've played Rampage World Tour, here are the updates: much better graphics, powered up punch, and a "Rampage" meter (which you don't know when you're going to hit it, it just shouts out Rampage and you glow red) which allows your punches and kicks to register more damage. The smash mode concept is the same, but you swing your arms down to smash instead of ground pound. However, I wish you the best of luck trying to pull off a smash with the Wii controls.
It does include the earlier versions, Rampage World Tour (from the N64) and Rampage (I think from the SNES??). I thought that was pretty sweet at first, and then I had a twinge of impulse to buy it, BUT!! while I was playing both earlier versions at different times, the sound crapped out on me and there was just buzzing and squealing. The framerate in Rampage World Tour slows down to where you are playing in slowmo, which would actually be a cool effect for a Rampage game, were it actually intended and not a shitty emulation job. In addition, playing R:WT on the Wii sucks because they've mapped "kick" to the A button, so you can't possibly run and kick at the same time unless you are a mutant and have an extra thumb sticking out of your hand.
So, having said that, if you find it for $5, pick it up. Otherwise, if you want a pretty Rampage game, try R:TD on the Cube/PS2/Xbox version. If you don't care about graphics, buy yourself the N64 cart, because I think that's when the game really peaked, and that would be money well spent.