The Red Army are now the only team to have won four from four in Europe this season after their 19-13 defeat of fellow RaboDirect PRO12 side Scarlets.
But despite James Coughlan's try and 14 points from the boot of Ronan O'Gara, Munster made heavy weather of beating a side they have had an Indian sign over in recent years.
And with the RaboDirect PRO12 swinging back into action on Boxing Day against Irish rivals Connacht at Thomond Park, McGahan has demanded they give the fans their money's worth on home soil.
He said: "You need to give the Scarlets credit for the way they came and played. There was a real conviction about how they wanted to play.
"We have a lot of belief in what we can do and what we can achieve. We want to be growing in this competition and taking the game forward each week, especially the way we fought so hard in the previous three rounds.
"Coming here, we were expecting a more complete performance. The players are disappointed with the performance.
"We really came here to improve what we have been trying to do. While we got through, we recognise we have a hell of a lot of work to do.
"The big thing for us is to control the scoreboard, but also the clock. We have worked so hard for our points and then let the opposition straight back in with three points and field position.
"If we have any thoughts of going any further in this competition, we need to make sure we recognise that."
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