Infested Planet was one of the best fivers I've ever spent - I was initially put off by the art-style, but it's not as bad as it seemed, and the core gameplay outweighs it massively. I love the planetary campaign mode, specifically cause you often find yourself having to adapt for lack of the particular units/structures/upgrades you tend to rely on. The strategy layer is very elegant in its simplicity, and I like how there's compelling consequences to retreating - Retain the army's morale -1, but you can't use them to attack for 2 turns. And having the enemy change up the game every few battles makes it very challenging, they have some really nasty abilities like the Vile Tongue, which spawns a group of towers in the centre of which is an alien that will grab your marines and drag them in until one or the other dies.
