How different is the Modern Warfare 3 engine to that of MW2?

Difference is “huge”, says Sledgehammer.
Since the release of Call of Duty 2 back in 2005, all subsequent entries in the series have been built on the same Infinity Ward engine. Despite the modifications that have been made to the engine with each new release, many commentators have started to speak up about it feeling and looking age – especially when compared to other, more modern, engines.
However, the general manager of Modern Warfare 3 co-develop Sledgehammer, Glen Schofield, has responded to the criticism – describing the engine as a “Porsche”.
“I’ll tell you one thing,” Schofield told CVG. “I’ve worked on a lot of engines over my lifetime and spent a lot of time putting graphics in to them and this thing is Porsche. And what I mean by that is that it’s stream-lined, everything in it is perfectly freaking clean. You can tell it’s been worked on for years. It’s easy to upgrade.”
He continued by describing just how MW3’s engines provides improvements over previous games:
“We worked with engines before that are like f***ing spaghetti. You can’t work on a part and put it back in without messing with everything else. Modern Warfare 3’s levels now are so much bigger than the old ones because they go more vertically, they have a bigger footprint and on top of that, higher fidelity, more textures and a lot more detail.
“If you put Modern Warfare 2 next to Modern Warfare 3 you would see a huge difference. Look at all the character models, look at all the gun models, look at the reflections, look at the water. There is so much that we’ve added, so when someone says ‘cut and paste’, I don’t even want to talk to them because they don’t know. They just don’t know. They have no idea.”
There you go, people. Don’t say anything bad about Modern Warfare 3, you have no idea.
Source: CVG