St Mary's is the civic church of Bury St Edmunds and one of the largest parish churches in England. It sits just beside the cathedral and abbey ruins, but it is not overshadowed by them: the long nave, fine timber roof, and confident late-medieval proportions make it a major sight in its own right.
The church is especially good if you like English parish architecture at full stretch. It has the size and dignity of a small cathedral, but with the local texture of memorials, chapels, and generations of town life layered through it.