‘And his feet (or legs) like burnished brass, as if it had been refined in a furnace.'
All the descriptions are seeking to bring out His glory, and John no doubt remembers the Transfiguration (Mark 9:1 and parallels) as he gazes at this heavenly figure. The translation ‘legs' (podes) is possible as the same word is used in terms of pillars of fire in Revelation 10:1 where it is descriptive of legs. But the usual meaning of the word is feet, and as the garment covers down to the feet, this would seem more probable here. (For OT parallels see Ezekiel 1:7; Daniel 10:6).
The actual word used here for brass is unknown outside Revelation, so that any Biblical parallels are only secondary. Undoubtedly it signified brass at its most pure and glorious, as is brought out by the fact that it has been ‘refined in a furnace'. In Isaiah 63 a glorious figure is depicted as treading down men in the winepress of God's wrath. In view of the parallel with eyes like a flame of fire, and its application to the partly idolatrous church of Thyatira (Revelation 2:18), such an idea may be in mind here (see Revelation 14:19-20), for all things are to be brought into subjection under His feet (Psa 8:6; 1 Corinthians 15:27; Ephesians 1:22; Hebrews 2:8).
‘And his voice as the voice of many waters.'
In Ezekiel 43:2 we are told that God's voice was ‘like the sound of many waters' as the glory of God came and the earth shone with His glory. This is clearly reflected here. Later the sound of heavenly voices is also described in these terms (Revelation 14:2; Revelation 19:6). So the voice of the ‘son of man' is as the voice of God and as the voice of a heavenly multitude, demonstrating His supreme power (compare and contrast ‘as of a trumpet' Revelation 1:10).