When Disney released "The Many Adventures of Winnie the Pooh" in 1977, it was a collection of shorts that Disney released in the 1960s and while some parts were added, they stayed relativily true to A. A. Milne's original tales. However, Pooh did not become the honey pot of gold for Disney until his TV series "The New Adventures" were released in 1988, and following the success of that series, Disney saw a trick and began pushing Pooh to the limits. The four films that followed, "Grand Adventure", "The Tigger Movie", "Piglet's Big Movie" and "The Heffalump Movie" all act and feel like the TV series instead of the 1977 feature and you can get a good feeling that Disney is spreading Milne's characters thinly here without using his adaptations.
The second one here, "The Tigger Movie" was the first one out of the four that got a cinema release (only the Great Adventure in 1997 was released straight to video). To be honest, that where this film should have belonged. Although Jim Cummings does a good job replacing Paul Winchell as Tigger, the voices from the TV series are all present and correct here, so you know that this isn't trying to be like the Many Adventures. While the humour is okay, the main story is on the verge of paper-thin and will do little to attract anyone above the age of 7. It is also baffling why Tigger wants to find his family. Doesn't anyone remember "The Blustery Day" when he sang about how proud he was that he was only one?
The animations is just a little more suped-up than the TV series. It is pretty much the same for the others. These films were made simply because Disney were pushing Pooh as their star franchise until around 2005 when they turn their attention to Princesses. While this should keep young kids happy, more true Pooh fans should stick to the Many Adventures or the shorts, and also maybe read more of Milne's original book stories.