Why is this game so charming despite being objectively the worst in its series?

It's an atmospheric mix between Doom and System Shock.

Nostalgia? I thought the way you use computers in the game was neat.
Did make it to the half mark point got bored and never finished it.
tfw you're an autistic coward and your little brother comes into your room, suddenly grabing you from behind while you play

If you ask me just about everything past refueling base just lowers in quality and enjoyability, probably a few exceptions

love Doom 3, yeah it is not as fast as the first two, but the atmosphere was all right

Get out.

...

I like The Chasm. I can't tell you why, but I like it.
All the others you listed are indeed shit, though.

Was the chasm the second to last? I thought that one was fun, especially after all the awful shit before it.

Wasn't that demon grey?

There are many words I can use to describe Doom 3, but charming isn't one of them. The game was a soul-less albeit impressive tech demo.