I have always assumed that it was rather obvious the Last Supper was a Jewish Passover meal. The Synoptic gospels make this clear, and I guess I just never thought that much about the fact that John's gospel suggests otherwise. And it is what I was always taught.
However, I just finished reading Pope Benedict XVI's book "Jesus of Nazareth, Holy Week: The Entrance into Jerusalem to the Resurrection". He devotes about 10 pages to this topic. He presents looks at various theories to the question (as you see in the whole book, treating all opinions with the utmost respect) and seems to conclude otherwise.
A couple of quotes from the book (pages 112-113):
The most meticulous evaluation I have come across of all of the solutions proposed so far is found in the book *A Marginal Jew: Rethinking the Historical Jesus *by John P. Meier, who at the end of his first volume presents a comprehensive study of the chronology of Jesus' life. He concludes that one has to choose between the Synoptic and Johannine chronologies, and he argues, on the basis of the whole range of source material that the weight of evidence favors John
We have to ask, though, what Jesus' Last Supper actually was. And how did it acquire its undoubtedly early attribution of Passover character? The answer given by Meier is astonishingly simple and in many respects convincing: Jesus knew he was about to die. He knew would not be able to eat the Passover again. Fully aware of this, he invited his disciples to a Last Supper of a very special kind, one that followed no specific Jewish ritual but, rather, constituted his farewell; during the meal he gave them something new: he gave them himself as the true Lamb and thereby instituted his Passover.
Well, I did a little searching on the Web about this question, and came up with this article by Jimmy Akins: jimmyakin.com/was-the-last-supper-a-passover-meal
Mr. Akins (and others) come down squarely on the other side of the question. In particular, they devote a lot of attention to the structure of the meal being similar to a Seder meal, and he even concludes with this
Thus John also understands the meal to be a Passover seder. Confusion suggesting otherwise is simply due to lack of understanding of the Jewish customs and terms of the time.
I believe Scott Hahn has written on this same subject and also favors what Mr Akins has said, in even more detail (although I don't have that in front of me right now).
In this regard, Pope Benedict, says
Yet Meier is right to point out that in the description of the meal itself,, the Synoptics recount as little of the Passover ritual as John. Thus with certain reservations, one can agree with his conclusion: 'The entire Johannine tradition, from the early to the late, agrees perfectly with the primitive Synoptic tradition on the non-Passover character of the meal'.
Of course I have a hard time attributing to Pope Benedict a "lack of understanding of the Jewish customs and terms of the time".
I am curious as to what some of our CAF experts on scripture say about this question. The Pope's book was fascinating and informative in all areas, but this was one part of it that really took me by surprise.