Ultimate War
A great flash turn-based strategy game by Anton Fedoruk, sponsored by arcadebomb.com.
I started thinking about ways of improving the game, and then I realised all I was doing was thinking of ways to make the game more complicated, and more like a 4X. So instead I've listed my ideas for how the game could be changed. I don't think these would necessary be an improvement, just a difference. I've listed these under ideas that will further complicate the game, ideas that will simplify the game, and ideas that neither simplify or complicate.
Complication
Units that can move more than one tile per turn (e.g. cavalry)
Ocean squares and naval units
More races
More unit types
More building types
Research
More players
Simplification
Remove buildings
Remove unit types
Other
Restrict production of soldiers/dwarfs/orcs to particular tiles (making it harder to reinforce the front line)
Increase/decrease the number of units that can be stacked in each tile
Make depleted units consolidate (allowing tiles to be further filled)
Make defensive structures more/less powerful
I also thought about the conceptual level about making games more complicated. Complexity gives the player more things to consider, more possible decisions. It can to an extent water down the impact of a bad decision, because the players are making more decisions in total. The decisions in Ultimate War are:
What to spend money on (Build units vs Build buildings vs Keep reserves)
Where to build/move units
Whether to attack or not (each turn)
It is possible to increase the complexity of the game by making these decisions more complicated (e.g. introducing new units) or by adding in entirely new decisions (e.g. diplomacy).