Some VGUs have been really bad while others have been spot on. Galio's VGU was awful and basically created a completely new champion. They could've kept the old Galio and added in the new Galio as a new champ and there would be almost no similarities between the two. Warwick's VGU was just spot on in every way possible. Kept the feel of playing old Warwick, but modernized his kit to help him fit in with the today's standards. GP's and Kat's were also really good imo.
The goal of a VGU should be to enhance a champion and not create a completely new one. There's basically no resemblance at all to the old Galio with the new one aside from the taunt. Basically a new champ all around. It seems like Swain might be the same way, but I never really played him and I haven't played the new one so I don't know. I can definitely understand why some people are upset about the rework. Having your champion deleted and replaced with a completely different one REALLY sucks.