Infested Planet is a mix between StarCraft and Starship Troopers.
I will start with the negative points first:
The difficulty can be quite extreme in the later levels. Despite a very flexible gameplay system and some good level ideas or even some maps that are randomly generated, overall the game can end up feeling repetitive if played in long sessions. The art style goes from excellent to just ok.
Now for the rest. Infested Planet plays like a tactical game, or a light RTS (Real-time Strategy). The base construction is minimal, as there is no resource harvesting and there are no factories. The buildings just provide defense or a specific bonus. They are definitively not at the center of the game.
However the distribution of the bases are an important factor of the game. Each base is actually a capture point that can belong to either the player or the Aliens according to who takes it. In general, the player starts with one point and will have to battle through the map and capture each point.
Each Alien base produces a continuous swarm of creatures that attack the player's positions (and despite some minor pathfinding issues, the AI is not stupid and can change course to attack undefended point). The player then has to manage the defense against the flow of Aliens, and the offense to capture points. Capturing a point has two effects that allow the game its sense of progression: some building points are awarded to the player in order to upgrade their army, and the Aliens benefit from a new mutation (new enemy type, new defenses, new hives) that increases the difficulty. Towards the end of the map, the Aliens are very powerful but the player has a wide range of options to deal with them and adapt to the mutation.
Adaptation is an important word to describe this game. First, because there are a lot of options available to the player. Different kind of weapons for the Marines to equip (Minigun, Flamethrower), or different buildings (turrets, airstrike, bonuses for the Marines or buildings). And even if it is more gamey than realistic, at any given point it is possible to remove one of these options to retrieve back all the building points that it costs and change strategy on the fly. This is really GREAT and it allows to experiment without being stuck in a specific technological branch, and to react better to situations (however, some bonuses feel lackluster in comparison to others and thus the cost of entry is not worth investing). Since I am praising this gameplay idea, I also think that the UI (User Interface) and gameplay and level design are all based on the RTS formula but with some nice and subtle improvement touches.
An example would be the dreaded escort mission that plagues most RTS games. Except that here, if the escort dies, it just respawns and tries again. Thus the escort feels like an additional firepower help until the map is safe enough to navigate it, instead of being a burden!
What I like with this game is its adaptability, its polished touches that are delightful surprises, and its sense of progression and pace. Every little step won or lost to the Alien swarms can be felt by the player, and there are very tense moments. And then the overwhelming scary swarm can suddenly be overturned into a jubilating victory, until a new mutation tips the balance of power.
Really a unique and interesting game that shows that RTS games can offer more than we think if they are well thought-of and if the developers are not afraid to make changes in the classic formula.