Build, upgrade and hold the line for fifteen waves — quick thinking is worth points
Tower defense is one of the most approachable strategy genres: enemies march along a fixed route, and instead of steering a hero the player builds fixed defences beside it. The idea goes back to early arcade and strategy titles, and it exploded in popularity in the 2000s with browser games and custom maps for real-time strategy games, because the rules can be learned in a minute and still leave room for clever play.
The interesting decisions are about money and position. A cheap tower placed early pays for itself, an expensive one placed at a bend in the road reaches more of the path, and slowing enemies down makes every other tower more effective. Spending on upgrades or on new towers, and deciding whether to call the next wave early for a bonus or wait and prepare, is the heart of the genre — and why two players on the same map can finish far apart.
Maps in games like this are often generated rather than drawn by hand, which keeps every session fresh, while a shared daily map turns the game into a fair contest: everyone faces the same road and the same waves, so the difference in score comes down to planning and nerve. Try a different balance of towers each time and see which combination holds up longest.