The Reds shelled out £20million for the Aston Villa winger who joins fellow new boys Jordan Henderson from Sunderland, Blackpool's Charlie Adam and former Roma goalkeeper Doni at Anfield.
And Liverpool's director of football is delighted with the capture of the England winger as well as the other additions - and cannot wait to see them training together for the first time on Monday.
On the Downing signature, Comolli told Sky Sports: "It is very significant, as significant as the others. I don't think we can make any difference. They are all priorities for us, the Liverpool players we've signed.
"Stewart we know everything he can bring to us but we are delighted to have signed the other three as well.
"Obviously he can play on both sides which is good.
"He can play different systems whether it's 4-3-3 or 4-4-2 or whatever Kenny wants to do, and then he brings us his strength - the quality of his delivery.
"He can score, he creates a lot, he can deliver a lot of assists so he was the missing link that we didn't have and that's why we were eager to get him.
"To have everybody on Monday is a comfort really. I saw Carra (Jamie Carragher) and Carra said about Stewart that he will come into the changing rooms knowing all of the players and I think that is very important."