Hey guys, I've finally gotten round to putting that demo together for Systematic Immunity :) You can download it on my website or on IndieDB.
The demo features the first 20 levels of the game, which should give a fairly good impression of what the game is all about.
The settings menus aren't polished at all yet, so sorry about the hideous interface there ;) Also, if it runs a bit slowly, I'd suggest turning the terrain highlights to low or off completely. Turning the bloom off will help as well. You can access these settings by going to the settings menu and clicking on Graphics Settings.
I'd also recommend playing the game with an XBox 360 controller if you have one. If not though the game is perfectly playable with the keyboard and you can change the keybindings if you want by going to the settings menu, clicking controls and clicking on the control you want to change and then pressing the desired button.
To install it, simply download the zip file. Extract the installer and run it.
If you'd like to get in touch with me with your feedback/thoughts I'd appreciate it a lot :)
Windows Vista/7/8, DirectX 9.0c and Shader Model 2.0 graphics support, 2 GB RAM, 2 GHz dual core Processor, 212 MB free hard disk space
Thanks and have fun!