Build this kind of game
Find the faction or unit that is simply better than the others in every matchup
With three or four factions it is easy to end up with one that nobody has a reason to skip, and another that nobody should ever pick. Players find this out within a week. Here is a check on a table of win rates that names both, before the game is published.
Keep a big simulation from freezing after the player switches tabs and comes back
Your city simulation runs at a fixed pace, but when the browser pauses the game for a minute, it tries to make up all the missed steps at once and the screen locks up. Here is the loop that catches up in a controlled way and what to throw away.
Keep the map you have seen dimmed while only what your units see right now is bright
A fogged map has three kinds of squares: never seen, seen before, and seen right now. Games get this wrong by hiding places again when the unit walks on or by showing a ragged circle. Here is the update that keeps the three apart and the circle clean.
Build a game where you only steer, your hero fires itself and crowds of enemies close in
In a steer-only survival game the player moves while the hero attacks on its own, picks up drops and chooses upgrades. The choices that matter are who gets hit, how pickups are drawn in, and offering upgrade cards that are never the same twice. Here is the loop.
Build a game where you play cards from a hand against an enemy that shows what it will do
A card duel runs on a draw pile, a hand, a discard pile and a small supply of energy per turn. The classic slip is a draw pile that runs dry in the middle of drawing. Here is a loop that reshuffles at the right moment and keeps every card.
Build a dungeon game where everyone takes turns and fast creatures act more often
A turn-based dungeon crawl waits for the player, then lets every creature act. Giving some creatures more actions than others fairly is where the fuss starts. Here is a scheduler that handles speed, bumping into things to fight, and death, all in a few lines.
Build a game where you run forever, jump obstacles and the pace keeps rising
An endless runner is a loop of speed, jump and spawn. The part that decides whether it is fun is an obstacle placement that is always beatable even at top speed. Here is the loop, with a rule for fair gaps and a way to prove it.
Build a puzzle game where pieces fall, turn and clear full rows
A game of falling pieces on a narrow board is a loop of drop, turn, lock and clear. It looks easy until a piece turns inside a wall or a row clears while the pieces above it hang in the air. Here is the loop that holds together, ready to build on.
Build a game of planting, watering and harvesting across days and seasons
A farming game ticks in days: you act, you sleep, the world moves one day. The tricky parts are crops that only grow on watered days, rain that waters everything, and plants that die when the season turns. Here is the day loop with those rules.
Build a game where things earn for you, prices climb and you buy more
A game of buying helpers who earn while you wait is a loop of income, price growth and the choice what to buy next. Its trouble spots are the price rule, buying many at once without a slow loop, and the time you were away. Here is the working loop.
Build a game where enemies walk a fixed road and your towers must stop them
A tower-and-wave game is a road, a stream of walkers, and shooters with a range and a pause between shots. Most bugs come from which enemy gets shot and from what happens at the very end of the road. Here is the loop with those decisions made.
Build a game where you swap neighbouring tiles to line up three and chain reactions follow
Swapping tiles to make a line of three is a loop of swap, find, clear, drop and refill, repeated until the board is calm. The details that go wrong are swaps that change nothing, lines found twice and refills that start another chain. Here is the loop.