Is it the tunes or the words or both that create the initial sense of "ooh, I like that" about a hymn, carol or song? 

The tune Winchester New, used both for "On Jordan's Bank the Baptist's cry" (BPW 147) and "Ride on, Ride on, in Majesty" has, for me, a strangely haunting quality, which combined with the juxtapostion of Advent and Passiontide combines beuaty with pathos.

The reminder that "the Lord is nigh" carries a very differentt sense this side of Calvary than it would have when John cried out in the wilderness regions.  God is at hand... the Lord is near... God's time is approaching... a variety of ways of reading/hearing this.

The hymn is overall pretty positive - we are called to make ourselves ready, but there is no big stick to beat us.  The echoes of Isaiah 40 are there in verse 3, along with hints of Isaiah 9.

Essentially, this is a hopeful hymn - the Lord is nigh, which is Good News!

On Jordan's bank the Baptist's cry
Announces that the Lord is nigh;
Awake and hearken, for he brings
Glad tidings from the King of kings!

Then cleansed be every life from sin;
Make straight the way for God within,
And let us all our hearts prepare
For Christ to come and enter there.

For thou art our salvation, Lord,
Our refuge, and our great reward;
Without thy grace we waste away
Like flowers that wither and decay.

To heal the sick stretch out your hand,
And bid the fallen sinner stand;
Shine forth, and let your light restore
Earth's own true loveliness once more.

All praise to you, eternal Son,
Whose advent has our freedom won,
Whom, with the Father, we adore,
And Holy Spirit, for evermore.

Jordanis oras praevia Charles Coffin (1676-1749) translated John Chandler (1806-1876)