Of course the nature of the celebration has changed a bit and having exported the festival to the USA we have re-imported some of the commercial American approach. Nevertheless it is a great night particularly for kids. Fireworks and bonfires light up the sky. Children dress up in costumes and visit their neighbour's collecting sweets and treats (the appellation "trick or treating" is an American import but the practice originated here). For Children it is probably the second biggest night after Christmas. There are even rumours of adults who still follow the old religions and celebrate a much more ancient version of Oiche Shamna in secret places.
Wikipedia has two very good articles here and here.
I guess my title is not a particularly apt salutation for the night that is in it so instead I will say:
Oiche Shamna scanruil dhuit