Like AXS, DreamStation's main differentiator is that it contains a tracker-type 32-track step sequencer. This may be useful for users who have graduated from using trackers and are used to that type of sequencer, but other users may find it useful for building multi-layer sounds with the different oscillators being triggered by different tracks.
The synthesizer iteself has 3 oscillators per voice with lowpass, highpass and bandpass filters, oscillator syncronisation, frequency modulation and distortion. There are also chorus, flanger, phaser, delay and reverb effects -- up to 3 can be used simultaneously. Features that make it stand out are that samples can be used in place of oscillators and there is also a formant filter mode (which can provide voice-type effects). It comes with virtual MIDI drivers to pass MIDI from, and more unusually to, your sequencer.
Audio Simulation claims that their SmartOSC™ synthesis library reduces digital aliasing and provides a quality of sound unheard of in this category. Well, the sound is very crisp, but lacks somewhat of a fatness and some depth - I would recommend it more for zaps and sounds that are meant to pierce a mix rather than pads and fat leads.
Though a freely downloadable demo is available, the full product costs $130. With the quality of software that can be obtained for free this feels a bit excessive, though it does have some unique features.