Inter have banged in 30 goals in 13 games since Leonardo took over but have also proved alarmingly leaky at the back, conceding 17.
In Italy there is much talk about the new attacking Inter, in complete contrast to the perceived defensive style they had under Jose Mourinho last season.
But van Gaal can't see any difference.
"Inter have not changed a lot, they had a few players injured at the beginning of the season and they still do now such as Diego Milito and Lucio, who is coming back, but in reality they're practically the same," he said here Tuesday.
"They've changed coaches twice (Rafael Benitez lasted less than six months as Mourinho's successor) and that's the biggest change.
"But the most important thing is that they haven't changed their way of playing."
When pressed on just why he felt Inter were a defensive side, van Gaal harked back to the Champions League final in Madrid in May where Mourinho's Inter ran out 2-0 winners.
"If you've seen the final then you should know. I don't know why I have to keep repeating myself," spat the Dutchman.
"If you see how they play every week then you can see that they are very defensive.
"Against Cagliari in the second half, Cagliari were very attacking and Inter shut up shop at the back, and that despite playing at home.
"But they're the champions, they won everything last season playing this way.
"They took the decision to play this way, the coach and the club did. I think differently, I want to play more attractive football to give pleasure to the fans and I think it's more difficult to play this way than to play defensively.
"We always play the same way, we always play to win and we won't play differently tomorrow."
However, despite his disdain for Inter's style of play, van Gaal insists it is the Italians who should be considered as the team to beat.
"The favourites are always the champions and Inter are the champions. They're also playing at home so that's another reason that they are the favourites.
"They have a great team, they're well organised. It's difficult for every team playing in Europe to play against a team like Inter.
"They have strong players like (Samuel) Eto'o, (Wesley) Sneijder and (Goran) Pandev, so I think they're the favourites."
However, van Gaal played down the effect Inter's victory in last year's final over the Germans will have in this game.
"For me it will have no effect at all. A final has nothing to do with a last 16 clash," he said.
"Our team has changed a bit, some players have gone and some others have arrived.
"It could play a bit on certain players' minds but as Bayern players they know that we always want to win and that will happen tomorrow as well, the final won't count."
Bayern vice-captain Bastian Schweinsteiger even believes that the fact this is a two-legged game will help his side.
"The difference is this is over two games, we've got a better chance of progressing," he said.
And the Germans' captain Philipp Lahm dismissed any talk about revenge playing on the players' minds.
"The final happened last year, you can't go back over the past," he said.
"Revenge doesn't seem right, we can't win back the title we lost last year."