Catalan at source is probably as different to Spanish as French or Italian are. But probably, centuries of stronger influence have induced more similarities: most people in Catalonia are bilingual.

Especially for those who don't speak either:

Spanish: "Hay muchas cosas", "Tenemos una vez" French: "Il y a beaucoup des choses", "Nous avons une fois" Catalan: "N'hi ha moltes coses", "Tenim una vegada" Italian: "Ci sono molte cose", "Abbiamo una volta"

I think it's a quite representative example of the kind of differences & similarities.