If you don’t have a lot of experience with space shooter games, Boss Battles is a great way to start. You control a space ship that you move anywhere on the screen with your finger. You have to defeat one of a half dozen bosses (you pick which one). You can go back and face the same boss in another round, but it gets a little tougher. You shoot down little baddies first to warm up and collect diamonds they spew as they die. And you gets diamonds as a bounty for defeating the boss. With these you can upgrade you weapons in different ways. The balance between upgrades and challenge is pretty even, slightly in favor of upgrades.
I have played this twice, and both times I keep saying “ok, this is my last round, then I’m turning it off” and an hour later, I’m still playing it. It’s just hard enough to keep you going, and just easy enough that with absolutely no practice, you can get through a lot of rounds. And the rounds are just similar enough that you can know what to expect, and just different enough that you get that little extra thrill from having defeated it.
The ads across the top are annoying of course. And you can’t buy a no-ad version.
Survival score: a good 2 hour chunk of play time every 6 months or so.