I'm not completely against sequels and spin-offs when done well and with respect to the original source material but I feel the Compilation does not fulfill in either case.
When it changes and retcons plot elements and history it can affect the originals. Case in point the Force from Star Wars. In the original trilogy its a mysterious pseudo-religious philosophy and element that adds a sense of mystery and wonder to the films. In the prequels, its defined as simple bacteria in your cells that give you psychic powers. Suddenly, its difficult to get the wonder and breath of depth from Yoda's teachings to Skywalker when you suddenly remember that the Force is just a simple biological organism and the line "trust in the Force" can now be changed to say, "Trust the bacteria" it sorta kills all the mystique of the franchise when the franchise continues to utilize the retcon as canon.
For the Compilation, a lot of the changes are minor but it goes against statement made from the original game. For instance, CC states (SPOILER)the war in Wutai was caused by Wutai refusing to have Mako energy from Shin-Ra. Its clearly shown that Shin-Ra is in the Mako manufacturing business. In the original game, Cid states the war with Wutai started back when Shin-Ra was still a weapons manufacturing company. They hadn't even learn how much profits they could get from Mako energy until after the events when Cid had his failed launch. (SPOILER)CC states that the war in Wutai ended before Cid's launch. Its a glaring error and changes a bit of the original cause we now have to change a few facts regarding history.
The major element that bother me about CC and this is a major error that does in fact makes you question the main game; is the story revolving around the Nibelheim Incident. Easily one of the most important scenes in the original game's story. (SPOILER)CC adds Genesis to the Nibelheim Reactor scene from the original, he goads Sephiroth into learning about the Jenova project and personally I feel Sephiroth's whole involvement with Genesis and Angeal should have given him a better heads-up concerning the truth of his own origins so I feel their involvement in the story cheapens Sephiroth's reaction. Not to mention we also had Genesis' forces attack both Tifa and Cloud at the reactor and the dialogue from the original story indicates, Zack met Cloud for the first time at Nibelheim whereas CC has them as bosom buddies before the mission even started.
What's the major problem here that affects the original story? If Cloud knew all this, why doesn't he talk about any of it in the original game? Course its obvious that Cloud couldn't remember anything that was made ten years after the original but I also ask why would you make such drastic change to a story element that the main game's plot hangs upon? They should have had greater respect for the source material. Now it throws the main story in question if we are lead to believe we must treat CC as canon so now we have to either come up with lame excuses as to why Cloud doesn't remember(SPOILER) Genesis being at Nibelheim throughout the original game or wait for a remake that is going to have massive rewrites to the story. It just seems backwards that VII has to be remade so it fits with the Compilation when the Compilation should have been written not to conflict with the original.