Actually you can't install Skype on HD2 (or any other Windows Mobile device), at least from official sources. (...)
HD2 has bigger screen, but the same resolution as N900, 800x480.
... Internet Explorer Mobile supports Flash, but offers an overall poorer browsing experience. So I think you will have to use both in daily life, choosing on a website-by-website basis.
...and the Maemo OS which makes it very similar to a Linux PC capability-wise.