Defense Grid: The Awakening

Very easy, just don't lose any Power Orbs and you probably won't have to worry about how many points you get.

Always try and make the enemy walk past your towers twice (once on the left, once on the right). Have a mixture of towers and upgrade them rather than have lots of green towers.

Don't waste resources fortifying on easy waves, try and save resources as you get bonus resources for the more you have banked. You also get more money by having more Power Orbs in your base. Spend big on the hard waves, when the bosses come.