Free: yes! Fun? Not so much.
I wanted to like Chapel 3-D, since old-school shooters like catacombs are very much my cup of tea. But, unfortunately, this game plays like an unfinished alpha version.
It glitches, the hit boxes are wonky, you clip or fall out of the map. Jumping on the wrong object, like the skulls right at the start, catapults you across the entire map--or out of it, if you are unlucky.
Menus feel bare bones. Controls are awkward, enemies underwhelming, weapons lack impact. Most enemies luck weird enough when they stand still, but much worse when in motion. that is when they aren't glitching and remain unable to move.
Last but not least: Be warned that you cannot save your progress. If you die, you need to start over.
While this could be fun as a roguelike game mechanic, unfortunately this game only has one static map that you will have to traverse over and over again each time you die, providing no fresh experience on restart.
In short, it may be free, but even though, there are better ways to spend your time.