For the money (currently $35) I am sure that you cannot buy a better VSTi. This thing is really good for users wanting to enjoy the really phat subtractive synthesis. This thing has 3 oscillators (with a good variety of waveforms), loads of envelopes and LFOs (pitch, filter, amp), as well as effects to really beef up your sounds (chorus, delay, eq). The sounds you get out of it are really rich. The midi learn funtion in RGC synths is excellent too...just assign knobs on your controller to knobs on the VSTi at the click of a button!
What I like about this synth is that it is the "not so little" brother of Pentagon 1, so when you are ready for a more powerful synth you are instantly familiar with its controls. If you've tried Triangle 1 or 2...you will love this! Hopefully the GUI of Square 1 will be updated soon so that you have the option of a P1-type skin in the next version.