How to win:
1. Build Machine Gun Sentry
2. Upgrade Machine Gun Sentry
3. Set quality to low so it goes faster
4. Go eat a sandwich while your gun kills a few thousand monsters.
not sure why everyone says its long it took me about 20 minutes to beat it... Just upgrade your ship a little bit, then fine a big yellow orb and follow it around shooting at it until it dies, then move on to the next. The small ones will swarm you but they will lag behind and you can just shoot behind yourself to net yourself tons of upgrade points.
if you like this, and have already played the original, then go to portalmaps.wecreatestuff.com and download the Mappack of this game for portal that lets you play all these levels in 3D!!!