What's a good iOS game for challenging tower defense gameplay with a futuristic theme?

If you're looking for a tower defense game that provides a good challenge and has a cool, futuristic setting, Galaxy Defense: Fortress TD is worth checking out. The game requires you to strategically place and upgrade your towers to defend against waves of enemies. What makes it engaging is the variety of towers and upgrades available, allowing for different defensive strategies. The futuristic theme adds to the appeal, creating an immersive experience as you defend your base against alien invaders. With its focus on strategic depth and challenging gameplay, Galaxy Defense: Fortress TD is a great choice for tower defense enthusiasts looking for something to test their skills.