We ate here twice while in Hanoi's Old Quarter. The first time for a snack (sesame fries), the second time for a meal. Whilst roaming the streets of the Old Quarter, at the mercy of Hanoi's humidity, The Real Kangaroo Cafe presents itself as somewhat of an oasis. It's air conditioned, with a pleasant atmosphere and staff.
In terms of food - between us, my wife and I tried their beef burger, veggie burger, sesame fries, vanilla milkshake and banana shake. All were reasonably priced, large in size and most importantly...quite tasty. The veggie burger wasn't particularly memorable, but the beef burger was second only to one I tasted at The Gourmet Corner. It was juicy and well-seasoned, as were the hand-cut (and unique) sesame fries.
I can't speak for the Vietnamese dishes, as we'd been Vietnamesed-out by a walking food tour, only that morning. Looking at other reviews, I'm sure they're quite good, too.
All in all, recommended.