The Trouble with Robots is a sort of single-player, sidescrolling trading-card game, with something of the feel of tower defense.
The backstory is that a flying saucer has landed in a fantasy world, disgorging innumerable robots. In a series of 20-something levels, you control armies composed of peasants, elves, centaurs, and the like against robots of diverse types.
Before a level begins, you select 5 cards from those available to you -- only a few choices are available at game start, but other cards are unlocked during play. There are multiple waves of attackers within a level; each wave, you are dealt new cards. Energy to play them recharges over time; you can use surplus energy to trigger lightning bolt attacks on individual robots, which means that, unlike so many tower defense games, you do still have things to do while attacks are ongoing.
The graphics have the feel of hand-drawn animation; there's a dialog between the fantasy creatures and the robots at the start of each level, and it's often amusing, e.g.:
CENTAUR: We have defended these forests for a thousand years.
ROBOT: Shoo, pony.
The TCG aspect does not lead to deep strategy; basically, you play all the cards available to you each wave, except in rare circumstances. The random draw by wave does mean, though, that you can be hurt by the luck of the draw; you may not get the cards you want. And tower-defense-like, you don't have much to do as you watch your little guys battle away.
Still, it's light-hearted, a little silly, and entertaining enough to hold your interest through what is a fairly short game.