Original and one of the best

In my opinion there are only 2 tower defense games that are absolutely essential on the Mac App Store, IBomber Defense & Sentinel 3. IBomber is the standard for tower defense games, with its WWII setting, and most TD games are basically a clone of this type of game except for rare exceptions like Sentinel 3. Sentinel 3 holds its own with its upgradable towers, unlockable weapons, and killer enemy waves; not to mention its amazing graphics, sound, and UI. The additions of a Commander (which makes you feel like much more a part of the action) and multiple gates to defend (which adds multiple levels of strategy to the game, with the new need of a possible fallback position) are what makes this game truely special. Though the Commader is provided to you from the start there are a TON of upgrades you can earn for him including weapons, new abilities, and his individual stats (health, weapons range, strength, firepower). The campagn consists of 20 levels with 4 modes of difficulty, so youll need those upgrades, and has a ton of replay value; not to mention the Classic mode (which is kind of like a challenge mode with set weapons and powers for different maps) and of course, Endless mode for all 16 maps. For 3 bucks this game is a steal, for the high quality of its gameplay/design and quantity of content its also one of the best games Ive bought on the Mac App Store.

Faragaut1945 about Sentinel 3: Homeworld