Nos is required. A nosotros is not. It is optional, for emphasis in this case. "Nos encanta esta fiesta" should be accepted.
I think in this sentence, the "a nosotros" is redundant. It adds nothing surely?
If it is not required, why use it? Are we actually saying "We really love this party!"?
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.
So does this tricky - some would say bewildering- concept of putting 'A mi/A nosotros' etc before the verb confined to just gustar and encantar? Or can it apply to all verbs?
So is it like nos encanta means we like and a nosostros nos encanta means we really like?
Why the heck is my answer "We love this holiday" not accepted?! La palabra "fiesta" también significa "holiday", no?!
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/
wait. So I said "we like this party" and it was wrong. Why? Is Like not strong enough?
It´s incorrect, not sure but sounds like we charmed ourselves in english and the meaning of love yourself can´t be used with encantar, it sound really bad. For that we use the word querer.