First of all, make no mistake, I ADORED David Tennant as the 10th Doctor, and I'll gladly sit down and watch any and every episode from his tenor (excepting "Love and Monsters"), but DAMN! STOP BASHING MATT SMITH! I hate these little fanbrats who can't accept the fact that The Doctor regenerates!
First of all, this is NOTHING new to the show. The Doctor first regenerated in 1966 from William Hartnell into Patrick Troughton. It was a brash, baring move on the show's part that allowed for it's longevity. They could have just hired someone like Richard Hurndall (who took over playing The 1st Doctor for the 20 Year Anniversary, "The Five Doctors", as Hartnell had passed away by 1983) to take over as Hartnell's replacement and continue on with the series without there ever being a "2nd Doctor". But no, they decided instead to hire someone that was completely unlike Hartnell and told him to play The Doctor his own way.
So Patrick Troughton did just that. Whereas Hartnell's Doctor had been a dignified, if grumpy, old man, Troughton was a much more playful, wily, and...well, let's face it, he was a truly EPIC troll. He was always messing with people to get their goads.
Then they did the same thing with The 3rd Doctor. While the 1st and 2nd were largely tricksters, The 3rd was a dandy and a fighter, a very Sherlock Holmes type character.
Then after Jon Pertwee left the series, Tom Baker came in, and... Magic was made. Once again, the Doctor's character was taken in a completely different direction from everything that can come before. The 4th Doctor best personified just how alien The Doctor was. He was goofy, snarky, hyper, restless, and yet underneath there was a keen mind and a boundless spirit. He also the most ruthless Doctor since the 1st.
The 5th Doctor was a more kindly, subdued soul, often to his own detriment. He would try so hard to reason with people who would not be reasoned with and tragedy followed him wherever he went.
The 6th Doctor was...seven brands of crazy, and he an ego the size of China, but underneath all the bluster there was a real heart of gold, perhaps the biggest one of all the Doctors.
The 7th Doctor was a real callback to the olden days of Doctor Who, when the Doctor was largely a clever manipulative mastermind who could use all the people around him like chess pieces to get what he wanted. Just praise whatever deity you prescribe to what he's on our side (usually).
The 8th Doctor was an optimistically giddy, fun-loving good soul...but beware the nice ones. The 8th Doctor is the one who ended The Last Great Time War by killing The Timelords and the original Dalek empire.
The 9th is the direct consequence of 8th's action in the final days of the War. He was a Post Traumatic Stress Disorder sufferer filled with rage and sorrow. He was someone who needed a Companion most of all, because I hate to think what would have happened if Rose hadn't softened him up. Still, there was a kind-hearted man who truly loved life and respected it in him as well, it just took his regeneration into the 10th for it come out again.
The 10th Doctor was an almost child-like innocent soul with an optimistic gleam in his eyes, but also an underlying sorrow left over from his previous incarnation. Kind, fearless, brilliant, and pacifistic, the universe worked against him on all fronts to break him, and break him the poor man, it did.
And then there's the 11th Doctor, scatter-brained, egotistical, prideful yet self-loathing, and like the 10th in many ways, but also with shades of the 2nd and 9th. He is a silly bow-tie wearing fellow who loves to spin in circles and jump and bounce around the universe like the madman he is. Of course, he has to smile. He has to smile to keep from crying. Look at the accumulated blood on his hands from all his adventures leading up to who he is now. If he wasn't silly and bouncy, the poor man might just try to hang himself. He's another one who desperately needs Companions to keep him company.
See my point yet? The Doctor regenerates. He did so in 1966, 1969, 1974, 1981, 1984, 1987, 1996, sometime between '96 and 2005, 2005, 2010, and will do so again whenever Matt Smith decides to move on. There is no point in holding onto The 10th Doctor so obsessively and hating on Matt Smith with such ferocity, especially since you have The Doctor's Regenerations to thank for David Tennant ever being able to take up the role at all. If the creators of Doctor Who hadn't decided to make The Doctor's appearance and personality change back in 1966 and just had another actor who looks and sounds similar to Hartnell take over the role, there would be NO 10th Doctor AT ALL. So stop bashing Matt Smith in a pathetic attempt to try to get the creators to being David Tennant back. It's not happening. Ever. The 10th Doctor is gone. The best you can hope for is a Big Finish audiodrama with him or a multi-Doctor episode on the show in which he returns for just that episode, but that's it.
So far, Matt Smith had done an excellent job playing the role. He gets the role, and frankly, of the recent Doctors, he's the most like one of the Classic Doctors. Give him a fair chance. Oh, and guess what, David Tennant loves what he's done with the role.
So in conclusion: The Doctor regenerates. Get over it. Without The Doctor regenerating, the show wouldn't have even lasted long enough to become a cultural phenomenon. The Doctor's regeneration is practically a national event in England, and because of this strong hold the series has in the hearts of British TV viewers, that it was deemed warranting of a Revival (and even if it did get a Revival without Regenerations into young men, it'd be blokes like Patrick Stewart playing the Doctor). Oh, yeah, and without Christopher Ecceleston bringing in the viewers in the Revived series's first season, it wouldn't even have lasted long enough for there being a 10th Doctor, either. So no matter how you slice, you can't have it both ways. You can be accepting on The Doctor's Regeneration because it got you your precious 10 at all, or you can just deny its place in the series even though it's what allowed for The 10th Doctor's existance at all.
So I end this rant with a quote:
"Wonderful chap. All of them." -Brigadier Alastair Gordon Lethbridge-Stewart, in reference to every Doctor, ever.