It's not THAT much cheaper than the Colossus, but then again most guys are saying the Colossus is $4k, and it's not if you actually get the price list to order one direct from Rhodes.
Some cool features the Gemini has over the Colossus (only what I can recall):
added gain stage/control knob on the Lead ch, a Voice switch (3 voicing options?), Bright is now electronically switchable and programmable
accepts more types of power tubes than 6L6 and EL34 (e.g. KT88, 6550)
remove fuses instead of 2 power tubes to drop from 100W to 50W (easier access)
tube fault protection circuitry
This is what I can recall based on the Rhodes Facebook page a couple months ago, Kyle can confirm whether these features are actually in the final production version.
I am also looking forward to clips, notably of the "new" gain stage.