Probably not the font itself but the environment around it when you see it?

You usually sees it as the default monospace typeface in an old windows environment, probably with no anti-aliasing and with low resolution screen. That combination is an eyesore.

Courier New in an modern environment, with modern text rendering and anti-aliasing on high res screen is actually not bad at all.

I see it in other people's PuTTY sessions. It's so bad.

Use Consolas, or Droid Mono, Lucida Console, almost anything.

Courier is so thin and terrible. Combine that with the default color scheme of most Linux terminals...ugh.

Maximize that terminal window on a 16:9 display when connected to a device that only gives 80 characters wide output as the final mail in the coffin.