Indie game storeFree gamesFun gamesHorror games
Game developmentAssetsComics
SalesBundles
Jobs
"Why not to make the game get harder each minute? Or you change weapon type each minute"

Those are good ideas, I guess you could also do score multipliers every minute and so on as well. Or challenges for under a minute that give you a boost or something.

Then there is also bonus/power-up lasts for one minute, or even a sports game with 1 minute timer for rounds or qualifying etc.

Ooh, single minute sports sounds super neat.  I might try that!