No, Katatonia is not a goth band, because they play Gothic/Doom/Death Metal, Alternative Metal/Rock, while goth music consists of Gothic Rock and its derived genres, like Deathrock, Darkwave, Ethereal Wave, and Coldwave.

However, they do have a significant goth influence and even have some goth songs in their repertoire, like "Scarlet Heavens".

If you want to dive into the goth music scene, some of the bands that might appeal to you if you enjoy Katatonia are Cocteau Twins, Lycia, and The Cure.