Here in England and Wales, the celebration of the feast, and the attendant obligation to attend Mass, have been transferred to Sunday.
I think that is an unwise decision, pastorally. It erodes our Catholic Identity, and the sense of a special feast. Also at a psychological level, I think that lessening the demands our Faith makes on us weakens our Faith.
The Ascension is one of the more complex events to understand. But one aspect worthy of our attention is the fact that it visibly expresses the Father's acceptance of the Son's sacrifice, thus completing it.
This is clearly in line with the pattern in the Old Testament; and also, as Fr Hunwicke has pointed out, with the theology of the Roman Canon (in contrast with the new Eucharistic Prayers composed in the 1960s ff).
Here is an Ascension Day treat: