I thought I'd be happy with the free version...but I was so impressed I forked out for LE w/OmniSynth within three days!
Anyway, the instruments: I have never, ever heard two such realistic guitars, the drums are nigh-on perfect (although I think I've got two rim-shots instead of one & a regular snare, but hey...) and the pianos & strings are as you'd expect, but particularly good versions.
You can add four simultaneous effects from a comprehensive list - I'm especially impressed with the 'Lo-Fi' compressor; I 've used it in conjunction with the 'Phonograph' crackle/noise generator to replicate an old 7" single played on a Dansette.
The GUI is fine: five minutes playing around & you'll be familiar with it. The context-sensitive nature means that the knobs' functions will change to suit each instrument. Plus, the online support is great - a dedicated KVR forum.
Great - if you haven't downloaded it already...