It's bad for shooting air force test charts and therefore "not good". If you like it so be it! One of my favorite lenses is a finely scratched with little coating left Planar on a beaten up Rolleiflex 2.8E I found in an old alley shop in Beijing about 12 years ago. The "signature" of this lens pales compared to perfect Planars I have on other cameras in terms of contrast and fine sharpness yet it's one of my favs for portraits and even some types of b&w landscapes. However most would look at it or shoot with it a couple of times and swear it off. I see it as one of my most treasured cameras and truly unique and special.
I have this lens you mention too and like it just fine particularly for the $20 I paid for it. Will it win any awards for wide open performance? No but it was never really meant to.