While we've already seen a leaked version of TouchWiz running on top of ICS, a new leak shows us what HTC is doing with Android 4.0. I know you're all anxious to see what it's all about, so let's just get that out of the way first:
It's worth noting that this is a very early test build, so it's subject to change before it actually sees any official light. With that said, you are able to flash this now on the HTC Sensation, courtesy of the RCMix Ice v1 ROM over at XDA. As far as bugs are concerned, consider this a very early alpha build, so there are definitely things that won't work as they should.