Yes, ICS IS an improvement over HC, but not all that dramatic a change. I'm sticking with it mostly because I can use the Chrome beta browser, which I love, and also because I've never attempted a downgrade to the FW.
For me, ICS is a dramatic change. I have lots of widgets on most of my home screens and ICS has completely eliminated the stuttering and slow response I experienced with HC ... it's smooth as silk now and kills the last (and only) "advantage" my iPad user friends liked to crow about.
Also, the stock browser is MUCH faster (with no more white blocks while repainting), and there are dozens of little tweaks that make the user experience more pleasant.
That said, I've experienced a few of the random "black screen" issues and one reboot that left my docked Transformer batteries dead. Haven't found a pattern yet (it's relatively rare), but once Asus gets around to issuing a fix, ICS will be pure creamy goodness