Defense Grid: The Awakening

If you are having trouble beating a level, replay it using only cannon and gun towers and see if that helps your strategy.

Despite being the most basic tower, the gun tower is a solid tower and should be the cornerstone of your strategy throughout the game. Cannon towers are also essential, and should be behind the gun towers since they do not suffer from line-of-sight issues.

An upgraded gun tower outputs the same DPS as an equal value group of level 1 gun towers. However, upgrading is usually the best choice due to the importance of positioning. The same is more or less true for other towers, although Cannons and Temporals do well at level 2.

Do your best to setup "kill zones" where you can have upgraded towers efficiently clustered around a Temporal and Command towers. Try to make it so that enemies pass by these towers twice.

Press "backspace" to auto-load a checkpoint. This is very handy when experimenting with using the least amount of money possible to stop cores from being picked up. You can go to a checkpoint before that by hitting backspace more than once (useful if it checkpoints at a bad moment).

While it is technically possible to build a maze with two exits and then rotate which end is closed and open (to force enemies to travel back and forth) it is unnecessary in this game and difficult to do.

Some levels will let you build large mazes but this is usually inefficient; use the free space to make an ideal kill zone.

Laser towers are powerful but useless against shields, so use one after your main cluster of guns and cannons which will take care of the shields. If you use more than one, spread them out so enemies get the full burn damage before getting hit again. Laser towers only need to momentarily strike an enemy to start the burn damage.

Inferno towers have a higher DPS than gun towers if they are hitting 3 enemies at once, but are bad against shielded enemies. They should be placed where paths make a sharp L-turn such that the flame will point straight along the downstream path. Concussion towers are great only if you can get the enemy to walk on both sides of them. Meteor towers are nice when you have filled the spaces near the alien path with guns, further spaces with cannons, and have much further spaces available. Some stages have more or less swarm units, so adjust your AOE tower usage accordingly.

Area of effect towers quickly lose their usefulness after a few waves if you don't upgrade them.

Missile towers are very effective against air. Usually only one level 1 per "air alien" symbol is plenty. Spread them out if possible to avoid wasted shots. Gun and cannon towers can also be used against air units.