During the day I would like to show case a tiny portion of the features that make Winstep Xtreme (and the Winstep Nexus dock) so special, as well as address some possible concerns:

First and foremost, all Winstep applications are 100% compatible with Stardock software. Second, Winstep applications do not replace any system components and they only skin themselves: getting back to 'normal' Windows is as simple as exiting the software. Third, the Nexus (dock) component of Winstep Xtreme is fully compatible with skins for all major 3rd party docks. This means you can use your existing ObjectDock, RocketDock, RK Launcher, MobyDock and YZ Dock themes without any modification to skin the docks in Xtreme and Nexus (but read THIS themes tutorial first, please).
So, what features are pretty much unique to Winstep software? Let's start with some of the eye candy...
Special Effects
Winstep Xtreme is packed with effects of all kinds - no other dock in Windows even comes close to what it has to offer in this department.
Icon Reflections
Icon reflections 100% dynamic, they always accurately reflect the source icon even if the source icon itself is animated, and the bottom of the reflection fades into the dock background. You can even specify the size of the reflections (i.e.; how much of each icon should be reflected).

Some themes are even able to take advantage of another feature unique to Winstep software: reflection clipping. Notice how the icon reflections in the above screenshot are 'mapped' to the round tiles and do not extent outside of it.
Mouse over, Launch and Attention effects
The dock component of Winstep Xtreme currently features 18 mouse over effects (more being added all the time):
Magnify, Flat Magnify, Zoom, Bounce, AfterGlow, Rock, Swing, Squish, Spin, Sonic Boom, Heal, Fire, Magic, Flare, Wind, Water, Teleport and Push.

All the effects listed after the Zoom effect can be optionally combined with the normal dock Magnify effect. Some of the effects, such as Heal, Fire, Magic, Flare, Wind, Water and Teleport, are called 'particle animation effects' - these can be customized in order to change their duration and even colorized.

In the next release, colorization of the particle animation effects can also be automatic and based on the dominant color of the icon behind it (similar to the glow effect behind the icons in the Windows 7 taskbar) - there is already a private beta available to registered Winstep users where this can be seen working. Non-particle animation effects can have their duration and amplitude changed.
All of the above effects (except Magnify and Flat Magnify) can also be assigned as the Launch and Attention effects. The Shelf (tabbed dock) in Winstep Xtreme is also able to use all these effects as the mouse over, Launch and Attention effects (except Magnify and Flat Magnify, for obvious reasons).
Blur Behind
Docks, the Shelf, Desktop Modules, Menus, the NextSTART taskbar, all these objects are able to take advantage of the automatic Blur Behind feature in Winstep Xtreme when running under Vista or Windows 7.

Blur Behind ensures that semi-transparent (i.e. see-through) dock, menu, etc..., backgrounds are automatically blurred where required. Without it, the content of your desktop would merge with the actual contents of docks, menus, etc, and make a mess.
The Fluid Surface and Fluid Reflection effects
These two effects animate the background of a dock and the icon reflections, in real time, with a sine-wave based distortion effect. When this animated distortion is applied to icon reflections, an illusion is created in which the icons seem to be reflecting on water or a liquid surface background.

The Fluid Surface effect, on the other hand, was meant to be used only with specific dock backgrounds: for instance, when applied to a grass tiled dock theme, the fluid movement made the grass look like if it was swinging on the wind. Or you could even use both effect simultaneously, for instance, with the Nx-Water Nexus theme that ships with Xtreme. With the use of overlays, this theme makes icons seem like they are immersed in water - turn both fluid effects on and the water background seems to bounce and splash in real time.
Turns out both these effects became more popular than I ever intended them to - I constantly see them used on Youtube videos about Nexus in dock backgrounds that are not particularly suited for these effects.
Of course, being animated effects, you have to see them in action to really know what they do.
The Water Ripple effect
This is a cool little effect: click anywhere on a dock or in the Shelf, and several water ripples emanate from the point you clicked on, just like if you were clicking on water.
The Menu opening animation effects
NextSTART menus can also be assigned several menu opening animations: Slide Down, Slide Up, Slide Right, Slide Left, Grow Down from Corner, Grow Up from corner, Explode, Fade In, Shake, Ripple, Fire, Flare, Heal, Explosion, Magic.

Since applications in Winstep Xtreme are integrated with each other, setting a specific menu opening animation in NextSTART means that context menus in the docks, Shelf, etc..., also use the same animation.