But the United director insists the Dutchman will be a success at the club.
United are on course for Champions League qualification after a run of two defeats in 16 Barclays Premier League games, but they have come in for criticism this season for their style of play.
Van Gaal also struggled to get his side playing well at the start of the campaign and Charlton reckons the 63-year-old - despite having managed Barcelona, Ajax and Bayern Munich - may have been somewhat overawed by the stature of United when he took charge last July.
"It's been just the way I thought it would be this season," United's all-time top scorer wrote in his programme column prior to Saturday's home game against Sunderland.
"A new manager comes in and has lots of things on his mind, a lot to think about at once, and Louis van Gaal was perhaps a little surprised by the enormity of the club."
Van Gaal enjoyed success at those three European giants - and with the Hollandh national side - so Charlton is optimistic about the club's future under the Dutchman, who is contracted until the summer of 2017.
"I am not worried about the season or the future," said Charlton, who scored 249 in 758 appearances for the club.
"I think we can look forward to some fantastic times here.
"There has been misfortune along the way - look at the injuries we've had, or the deflected goal at Swansea last weekend - but sometimes you get that."
Source : PA
Source: PA