The SQ-1 is one of those synths from the late 80's/early 90's that you can often score for cheaper than the keyboard stand that you'll put it on. It's got Ensoniq's "Transwave" samples as well as about 100 other sampled waveforms that can be layered three to a voice. Each waveform has its own set of classic subtractive synth parameters - filters, ADSR envelope, etc. What's nice is that all the edit screens have a dedicated button to access them, so there's not too much scrolling through menus to get where you want to go. It's much easier to edit the patches on the SQ-1 than on a Planet Phatt, for instance. It seems to do best on big round organ sounds and punchy electric pianos, but if you combine some of the stranger waveforms, you can get some really hard, distorted-sounding synth effect tones that could be good for acid-house type stuff. It also has some drum sounds, half-decent but not worth getting excited about.
The on-board effects are actually much better than on any similar-era keyboard that I've used. They play a major role in determining the overall sound of the patch, much more so than on, say, a Kurzweil. The phaser the chorus are particularly rich and have a useful range of parameters, but for natural reverb I'd probably stick with an outboard unit.
The real fun, for me, is with the sequencer. It's integrated very well with the synth so as to make jamming and looping really intuitive. It's much more fun to just mess around with and generate ideas on than a software sequencer because the workflow is so effortless that you never really have to stop playing to set stuff up. Unfortunately the note capacity is only 9,000, but there is an upgrade chip that you can install to get up to 50,000 notes, which should be plenty considering that there's only 8 tracks.
Overall, for a workstation synth that can usually be found for under $200, the SQ-1's got solid tone and isn't nearly as annoying to operate as most of it's 90's peers. Plus it's made entirely out of metal (except the keys of course) so it won't fall apart after two gigs, unlike the cheapo plastic synths that everyone makes these days. The only downsides: no resonance on the filters and no aftertouch on the keyboard.