Metal Gear Solid has always been a mixture of combat and stealth, btw. Splinter Cell Conviction was adding this high-octane combat to a game that was ONLY about stalking, and planning.
MGS, since the first game, has always forced combat-heavy moments on you. From the elevator scene in MGS1, to the Frog encounter in MGS4. And those aren't even boss fights.
Add a tighter control system, and more uses of combat is simply refining something they've been doing since... forever. Comparing MGS to Splinter Cell is just nonsense, as they've never been anything alike, and they still aren't.
The stealth being based in the dark is really the only similarity in the MGSV demo that I saw to Splinter Cell. And as a huge fan of the series, it's a welcome change. Darkness is a huge factor in real stealth, and I'm glad MGS has finally incorporated that. Snake still has quick, defensive movements, like when he dives out of the way of the spotlight. It's basically the "roll" function that's been around since Metal Gear Solid 2, but it looks less conspicuous. Then there's the crouch walking, which has been around since MGS4. It was also a welcome addition to the series, because it offered a bridge between crawling and running around. All MGS has been doing with these changes is making it's stealth system more believable, when, let's face it, as much as I love MGS, Snake is as sneaky as a nuclear explosion.
Metal Gear Solid has been redefining itself with every new game that's been released. Each story has it's own tone, each game has it's own mechanics... this has been a trend since the beginning. Metal Gear Solid V looks absolutely INCREDIBLE, and if you really pay attention, you can see that just about everything they've added to Snake's movements is just a fine-tuned version of what he's been doing since the first game. Making the game open-world is an interesting choice for such a series, but it also opens up countless opportunities.
And finally... Keiffer Sutherland is not Snake. That is the only change that legitimately pisses me off. I'll give you guys that one.