Encantar is a tricky verb, used like gustar. So the normal rules are changed. What we are literally saying is "(to us) this party enchants us". Encantar has a stronger meaning than gustar, closer to "love". So here "this party" is the subject. "Nos" and "a nosotros" are the objects. "Nos encanta" is the bare minimum (it enchants us). "A nosotros" is optional and used for emphasis. Like I say, it's all tricky.
My son explained this as a reflexive verb. It is referring back again the the person indicated. And is more common and proper though redundent. As for me, i ... As for him, he... In some cases the first pronoun can also not be considered specific enough so the relexive prounoun clarifies exactly who is speaking.
It´s correct, fiesta can mean also holiday. Fiesta Patria, is for example the independence day, or flag day. And Las Fiestas we use to refer to the last week of the year Chirstmas and New Year. Without a context your answer can be accepted, but the expresion amo esta fiesta, sounds more like i love this party.
I found this helpful: https://www.fluentu.com/blog/spanish/verbs-like-gustar/
I speak English, 3 dialects of Chinese, studied some German and now learning Spanish. Every language has some tricky part. I love that Chinese has no grammar (I am bad at it) no plurals, conjugation, conjunctions, irregular words, formal tense or tense in relation to time. But you have to learn tones, (I'm tone deaf) 1000s of characters, time aspect and possibly different spoken and written forms of the same language. Spanish has latin grammar, the best thing is to say "Well this is the hard part. Ok. How can I best deal with it?". If we dot it's really easy to become discouraged. Languages are so complex I am surprised how well this app works. And the comments always help. Don't give up, you'll make it. :)
I don't understand why people are being downvoted for saying the truth. After weeks of teaching us "nosotros encantamos" it suddenly does a 180 and brings out all these new words, and we're just supposed to memorize it all without question or trying to understand what and why and when to use? Seriously...