I don't entirely concur with the hatred for the regeneration of 6 into 7. If Colin wasn't going to come back to do a regeneration story (and I don't blame him at all, I think he was treated very harshly), then they did what they could. I think the blurry effect on McCoy's face was alright, for the time.
I think it was more a case that they could have come up with a more dramatic, or interesting way to do it. The fact that Colin wouldn't come back and they improvised with McCoy wasn't, I think, the problem. In fact I think it was a brilliant idea to use McCoy and, frankly, it goes by so fast you can't really tell the difference. And perhaps that's why it was so abrupt -- so there wouldn't be anyone going "that's not Colin!". But I think they probably could have come up with a better way of handling it in terms of overall story. As it is, because the cause of the regeneration is so obscured, you get absolute silliness (apparently even supported by BBC-licensed matter) like the suggestion the regeneration was caused by the Doctor falling off his exercise bike! Aside from being stupid, it was also an insult to Colin Baker and his incarnation of the Doctor.
(That said, I just remembered David Tennant's line in The Next Doctor about hoping he wouldn't die from tripping over a brick. It would have been brilliant if he'd said falling off a bike instead...)
Alex