From Wikipedia:
The title ...And Then There Were Three... is a reference to the recent departure of Steve Hackett, reducing Genesis to a trio (which would result in their longest unchanged line-up, which lasted until 1996).

The album reached No.3 in the UK Albums Chart, and remained in the charts for 32 weeks having been bolstered by the UK Top 10 success of "Follow You Follow Me", which also became Genesis' first hit US single. ...And Then There Were Three... reached No.14 on the US chart, becoming their first Gold (eventually Platinum) album there (see RIAA certification).

While many of the songs were still progressive in terms of instrumentation and lyrics, the arrangements went from the more classical, movement-style composition of previous albums to the more standard verse/chorus/bridge format of popular songwriting. This was the final Genesis album to use a Mellotron.

Lyrics:
Lay your body down upon the midnight snow,
Feel the cold of winter in your hair
Here in a world of your own,
In a casing that's grown
To a children's delight
That arrived overnight.

And here they come to play their magic games
Carving names upon your frozen hand.
Here in a world of your own,
Like a sleeper whose eyes
Sees the pain with surprise
As it smothers your cries
They'll never never know.

Hey there's a Snowman
Hey, Hey what a Snowman
Pray for the Snowman
Ooh, Ooh what a Snowman
They say a snow year's a good year
Filled with the love of all who lie so deep.

Smiling faces tear your body to the ground
Covered red that only we can see.
Here in a ball that they made
From the snow on the ground,
See it rolling away
Wild eyes to the sky
They'll never, never know.

Hey there's a Snowman
Hey what a Snowman
Pray for the Snowman
Ooh, Ooh what a Snowman
They say a snow year's a good year
Filled with the love of all who lie so deep.

Hey there goes the Snowman
Hey,hey there what a Snowman
Hey there lies the Snowman
Hey he was a Snowman
They say a snow year's a good year
Filled with the love of all who lie so deep.

Hey,there goes the snowman
Hey,hey there what a snowman...