This app was mentioned in 12 comments, with an average of 2.08 upvotes
And because bot can't find Anomaly Warzone Earth.
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If you're asking for a game without IAPs:
Anomaly is fun. It has sequels as well, but I haven't played all of them.
The original Anomaly Warzone Earth
It is one of the rare games that runs really smoothly on the 5X and is fun
Anomaly Warzone Earth ran beautifully (both in terms of visuals and performance) on my old 600Mhz phone. Great game - basically reverse tower defense - cleverly adapted to touch controls, should easily run on your significantly more powerful device.
Air Control Lite is a much more simple game, but still a great time-waster.
Frozen Bubble, an old open-source classic that someone ported to Android. It's a timeless puzzle game.
Plants vs. Zombies. Another classic. Looks great, runs on any device, will keep you busy for weeks. Avoid its IAP-infested successor at all costs! This game does have IAPs, but they were added later and are not part of the original game design, as far as I know.
Minecraft Pocket Edition. Try the demo first. It scales very well and should run just fine on your device.
ScummVM allows you to play those old Lucas Arts adventure games on your phone. It doesn't come with any games, but you can e. g. purchase them on GoG. Since those games are mostly from the first half of the '90s, hardware requirements are very low.
Terry Cagangh's games are inventive, clever, minimalistic little masterpieces. Super Hexagon and VVVVVV in particular are absolutely fantastic, stand-out titles you shouldn't miss!
Anomaly games are fun TD games. It reverses the role as you're the mobs attacking the towers.