You can't just toggle Sense off - you'd need to install a whole new ROM, which you don't want to do.
But you can run a different launcher, or home app, on top of HTC Sense, in place of the default Sense launcher. The launcher provides the user interface part of the ROM.
Try something like 'nova launcher' - it looks more like ICS was meant to. When you run it, you can change the nova settings to make it the default launcher app.
Nova's just the one I use - there are lots of others that might be more like what you want.