Touchwiz +
Best lockscreen ever in an Android phone. Better than even 3rd party lockscreens.
Best notification bar rendition, with dark grey themes, color markings on icons, and four widgets in the bar. Very convenient.
Edit Homescreens. Lets you switch the order of the homescreens. I love this part.
Side by side swipe of the application screen. Its not as choppy as the up and down scroll of the app screen in other phones.
Keeps more stuff stock, like Contact Shortcuts and the Photo Gallery.
Best damn music player I've seen.
Nice clock widgets
Daily Briefings and Updates
Now for
HTC Sense
7 homescreen pinch - Love this effect
Best widgets, like the weather and the rollodeck clock that is HTC's signature item.
Scenes -- lets you save your custom homescreen, try out different homescreen preset templates, and so on. Big plus here
Streams for Twitter, Facebook, Google News and Google Reader. In some regions, also offers MySpace or Plurk.
Among the best Google news widget that comes with a phone
Aesthetically more appealing, though its HTC's black and white themes vs. Samsung's love of using neon.
While this works only in some apps, HTC Sense has a clever select tool text for cut and paste.