A very simple to use VSTi that does exactly what the name suggests. There aren't huge numbers of presets, but who need them for a piano? There are enough parameters to tweak for a bit of variation, such as 'hardness' and 'muffle' and flat or sharp tuning, so you can get a good-ish reproduction of pedal use and timbres, and nobody would need a manual with this thing - it's too straight-forward to need one.
It sounds better than any S+S workstation piano sounds I've ever played with (including the famous Korg M1 - which was excellent, but only suited certain styles IMO), and can be used in almost any mix or style. It can't compete with a full sampler, but for most people it will be perfectly good enough, and only true orchestral types will complain about the sound.
Add a little reverb and it will cover over any imperfections you might hear (not that I had any complaints with the dry sound anyway). Considering it's free, it is an amazing VSTi, and competes with most of the piano rack modules that came out a few years ago.
It's very reliable and you'll barely register any CPU useage, so no need to save power and record to audio.
I've always wanted a decent piano sound and can't get it on any of my hardware synths, but never considered it worth the several hundred bucks to buy a module. This fills the gap perfectly.
Everybody needs a piano at some stage, and this is it. I scored a few points off it for features and presets, but really that's irrelevant, as it is a piano - if you need envelopes and filters, then put it through some plug-ins to make it un-piano-like (?) but why would you want to?
Simple, reliable, uncluttered, clean and a VERY good emulation of a piano - it does everything it should.