Click on photos to enlarge.
Notes in italics from Oxfordshire by Jennifer Sherwood and Nikolaus Pevsner (1974)
Yale University Press, New Haven and London.

An earlier church on the site dedicated to All Saints was rebuilt c.1432 by the Earl and Countess of Suffolk. (He was created Duke in 1448. The de la Poles were a merchant family from Hull. She was the grand-daughter of Geoffrey Chaucer. See her tomb and effigy below).
The early C14 tower survives from the previous church ... Bell-openings with cusped Y-tracery, and, unusually, pairs of bell-openings to E and W. The W window in the middle stage is C15. The outer walls of the church are of flint and stone set in a chequer part on the E wall; the embattled parapet is of brick. ... the N porch was rebuilt in 1832 re-using the original openings. Connected to the tower a covered passage leading to the almshouses west of the church.  

The continuation of the clerestory and the nave arcades into the chancel, unbroken by any chancel arch, results in a strikingly spacious and unified interior. The only division between parts of the church is by carved screens  ... The arcades of the chancel open to N and S chapels. That on the S, dedicated to St John the Baptist, is the chapel of the almshouses. The chancel and the N side of the nave were begun first ... The mouldings of the arcades are more elaborate than those on the S, and in the spandrels are angels bearing shields ... The roof rests on stone figure corbels ... Screens, C15.

The chancel E window of five lights has panel tracery ...
Second picture, the west end of the interior with the arch from the early C14 tower - double-chamfered and half-round responds.

Font. An octagonal bowl on a base panelled with blind ogee arches. The spectacular wooden cover ... was presented by John Duke of Suffolk after the death of his mother in 1475. 10½ ft high, it consists of four tiers of cusped and crocketed arches with the figure of St Michael at the apex. ... 

In the Chapel of St John is an impressive display of Late Gothic ornament. ... On the N is the tomb of the Duchess of Suffolk, with much flamboyant carving, painted and gilded ... The chapel walls are diapered with the sacred initials I.H.S., with the decorative effect of a Gothic tapestry. The diapering is repeated on the timber roof, which is enlivened by feather-bodied angels with outspread wings at the intersection of the beams.  ... Altar in St John's chapel by Sir Ninian Comper, 1902. The frontal and reredos have holly scrolls and figures on a gold background.
...

Alice Duchess of Suffolk, died 1475. (Grand-daughter of Geoffrey Chaucer). An alabaster effigy with long aristocratic features, like a horse's. She wears a coronet and simple robes with the Order of the Garter on her left arm. Pillow supported by four angels under an elaborate canopy. Angels too under double ogee canopies around the sides of the tomb. Behind the traceried openings on which the tomb-chest stands is a memento mori, a wizened cadaver, ... a grim example of the Late Gothic love of the macabre. ... Much of the colouring on the tomb is original, and the carving is of the highest quality. ... The canopy has a deep frieze with half-figures of angels, their wings outspread and over them a band of quatrefoils and cresting. Four pinnacles on each side of the tomb bear wooden figures of monks and angels (best seen on chapel side in previous row).

Thomas Chaucer (son of Geoffrey Chaucer) died 1434 and Matilda Burghersh, his wife, 39 and 38 in. effigies on a tomb-chest with a fine display of heraldic shields around its sides.
For an extensive scholarly article on the shields, see here at the website of the Oxford Architectural and Historical Society.