I bought this game for $0.49 a while back. I haven't finished it yet, but I think I have a pretty good idea for this recommendation. Ctrl+F "TL;DR" to skip reading.
Nimble Quest is also available as a free-to-play game on mobile devices, and that's where I'll start. Your purchase on Steam gives you the "Red Gem" DLC from mobile for free, and there are no microtransactions after that. You can't pay real money to unlock additional heroes or to buy more tokens. There isn't a demo of this game on Steam, but you can try it for free on iOS/Android if you have a compatible device.
The gameplay is pretty simple. You start with a small roster of three heroes, of which you pick one to be the leader. You start in a field and your ever-moving hero runs near (not into!) some enemies and starts attacking until they explode and vanish, leaving behind a gem you pick up. Or maybe there's a powerup that gives you a temporary boost. Or another hero. Picking up the hero adds one 'car' to your train and also amplifies your attack power, but also gives you a tail to worry about. This is an arcadey RPG Snake mashup. Kill enemies, gather heroes, get gems and tokens, power up, and die. Aim for the highest kill counts and gem collections! Clear stages to unlock more heroes!
Since this is a game of Snake, you have to mind the walls and your own tail. If you run into a wall, an enemy, or if your leader gets hit too many times and runs out of health, you die and Game Over. Assisting heroes have the same mortality concerns, so it's very possible that an enemy train can cut through yours and kill several allies. And your leader running into your train will kill the assisting heroes you touch, so careful maneuvering is key. I found keyboard controls much better than swiping on mobile, and you can even use a controller if you wanted. Controls were WASD or the arrow keys to move, Enter and Escape to pause.
The big part of the game is killing things to get gems. Clear a stage, get a small bonus of more gems. Green gems are worth one, blue five, red ten. Gems go to boosting powerups, giving heroes permanent upgrades, and buying tokens. Powerups range from instant enemy-killing bombs to freezing all enemies in place to a potion to heal allies of damage. All of these upgrades are pretty costly, but that's the name of the game. And having the Red Gem DLC already means it's going to go somewhat faster than F2P. Tokens are used for buying continues when you game over, entry to the Arena, buying buffs that last the current run, buying random unlocked heroes in the between-stages screen, and to skip stages you've cleared already.
The stages are square for the most part, with some exceptions like Graveyard having some obstacles or Courtyard having small alcoves, but the enemies are more interesting. You have damage-sponge knights with big swords, or stationary archers that'll shoot arrows at your allies, or healers who don't attack but will heal enemies you haven't killed, or fast-moving rats or so on. You have the same if smaller variety of heroes, though they shine a bit more with upgrades since they can do different things like explode and take out enemies on death, or soak even more damage, or heal on dealing damage. There don't seem to be any boss battles in this game.
Difficulty is pretty linear. The game starts out slow with spawns and introduces new enemy types at a decent rate, but you'll quickly have to learn how to manage multiple enemy trains and your allies' HP. You'll run into some cases where you just can't advance through a stage without spending gems on upgrades or tokens on buffs, but in the latter case, the game at least is pretty generous on its drops. You can also earn tokens through the game's only form of 'multiplayer' in the Arena. You're put into a Guild to start, which is nothing more than "#NAME" or whatever, but the game autopicks a hero you may or may not have and then a set of enemies and you just aim for the high score. You don't play with anyone, but it's a form of co-op if you think about it. Depending on how well you did in your guild and how well your guild did worldwide, you get a payment in tokens.
I also thought it was a cute touch with the descriptions you get on how you died, like "Merida tried to knock over a healer and lost" or "Uther made friends with a hairy rat" or so on. There seems to be a death description for every stage and every enemy, possibly for dying to its attacks and for running into it. It was also a nice touch how the hero sprites change slightly with each upgrade, like Ulrich's armor getting golden additions and his sword getting bigger or whatnot.
TL;DR: For 49 cents, this game was a steal. $5 may not be so bad, too. It's got pixel graphics, tight control, decent music, and there's quite a bit of replay value. There is a good variety of enemies to kill and be killed by, and buying upgrades does have a noticeable effect on your heroes and powerups. It is admittedly grindy and can be repetitive, but I don't think it's a game you can just sit down and play for hours on end. It's perfect for if you have to wait for another game to install or update, and you might find yourself playing a little longer than you expected, trying to beat your last high score or get just enough gems to get that upgrade you've been wanting. I know I didn't pay much, but I really got my money's worth out of the game. And I'm still not done.