Article with Navidad? Nochebuena?

Hola Pat

With gustar it's always compulsery to use the article. Here Navidad is the subject of the sentence: La Navidad me gusta mucho. You always need the article here, like in "Me gusta el chocolate" (not me gusta chocolate) or "Me gustan los cielos azules" (not me gustan cielos azules). 

However, in "en Navidad", we have a different functionality, we have a time phrase, an adverbial expression of time. In this case, we can use it or omit it (you can also say "en la Navidad"), but we have "fixed time expressions" that sound more natural to us not using the article. Other fixed time expressions with no article are "en verano" (in summer), "en Nochebuena" (on Christmas Eve), "en Semana Santa" (in Easter), etc.. 

I hope this clarified it for you. 

Saludos cordiales

Inma