Town were unable to build on their FA Cup heroics against Liverpool and two first-half goals from the Gills against a much-changed Salop side did the damage.
Ricketts refreshed his starting line-up with five changes for the League One clash but Shrews - six without a league win - were well beaten in Kent and only improved late in the second half after more changes.
The Town boss admitted his players could not compete in what he thought felt more like a game of rugby than football.
Ricketts said: "I'm disappointed with the result. We went from Sunday, a real football game, to a rugby game.
"We weren't built for that. We started OK, the pitch didn't allow us to pass - it's not an excuse because we could've done better.
"But it ended in a rugby game and ultimately ended with me having to put Omar (Beckles) up front because we couldn't get the game flowing at all.
"There were probably four or five passages we actually passed and as soon as we did that we hit the post, had one off the line and (Aaron) Pierre hit the side netting.
"But ultimately I'm disappointed we couldn't play our game. We went from a really good footballing game on Sunday where we were excellent to a rugby game we're not built for but could've handled better.
"I'm just disappointed it wasn't a game of football and I felt sorry for anyone who paid to watch the game."
FA Cup hero Jason Cummings again had to make do with a place on the bench while Ollie Norburn was missing due to the knock to his knee sustained against Liverpool.
Ricketts added: "He makes such a good impact off the bench. He enjoys that impact. We're keen to get him playing. I had an idea that it wasn't going to be a football game so we tried to go more robust."
With less than 48 hours left of the January transfer window it is understood Sunderland's interest in skipper Norburn has cooled and he appears to be remaining at Montgomery Waters Meadow.
But Ricketts, who insisted his 16th-placed side are 'not a million miles away', revealed that a couple of additions and departures are imminent, with Fejiri Okenabirhie's transfer to Doncaster set to be rubber-stamped.
He added: "There'll be a couple of additions and one or two outgoings in the next day or so because as much as anything we're into a really busy period.
"We only have six free weeks, we're really busy, we need players to get us through that and to add quality."