Tesla vs Lovecraft can be a very fun game. Tesla vs Lovecraft, unfortunately, can also be a relatively frustrating game. Get it on sale or from a bundle.

While nominally the goal of non-boss levels past the first few tutorial is to get rid of all enemies, more often than not the spawn rate will be higher than what you can do on your own, so your aim is to kill the large mobs and survive until the game decides (there might be some relation to how you use the mech, but it's not explicit) you've done enough to hand you the win. As you do this you "level up" by killing enemies and get various perks, and collect along the way both weapons, limited cast abilities, and timed powerups. You also collect mech pieces which give you a brief use of said mech, which provides moments of reprieve.

While there's some use to strategy (in a mix of your positioning within the map, priorities of what to collect or kill, and which perks you pick and how you use them), in practice you're either mowing down mobs in relative comfort or getting absolutely wrecked, with RNG for good weapons/perks saving you from the areas where the latter happens.

I guess my biggest complaint against the game are how the persistent upgrades are set up. While once you beat the game you do get access to much larger amounts of it, I do think their balance isn't optimal. This is probably a vestige of the game's parallel release in mobile platforms where the allure of these is getting players to pay for the currency rather than grind for it, but I did wish more than once that these got unlocked organically.

Core campaign is a relatively short affair, and afterwards there's NG+ and NG++, which are longer by virtue of those occasional levels which you fail over and over. But the thrill of the levels where you are the one keeping the mobs in check hits the right Pavlovian spots.