Don't listen to a Marine on this knife, they're brainwashed on it. :)
Kidding, really. The Marines are a little bias on this knife, but for good reason. It has been standard issue since before WWII, just like the 1911A1, and for good reasons. It is simple, strong, effective, and easy to use (all big pluses in combat). People may joke about the Corps, but they know a good thing when they see it. This knife is almost as tough as the men (and women) who use it. Since I wasn't in the Corps, I didn't get this toy to play with. Instead, I got a crappy little dagger that you could take apart, lose pieces of, would break its plastic handle, and so on. Trust me, the Corps knows what is good. When it comes down to survival, this knife is one of the best, even to be 50+ years old.
The new versions may improve it or not, depending on your view. There are some great knives out there, but the K is one of the best and at a solid price too. I carried a pocket knife they made for decades, before I decided to retire it before it was lost or stolen. That little sucker was a lot less knife, but lived up to its bigger brother.
I've heard some say that there are "better" knives out there. I've even seen some with prices hitting the $500 range. Exotic metals, handles, fancy sheaths, the whole nine years. But, if you keep it simple, you rarely go wrong. A fancy knife is good in a collection, but a service knife doesn't have to be fancy. If you lose a K, you can replace it cheaply and still have a great knife, just like the lost one. If you know your knife, inside and out, then you can do a lot more and know you can do it, without counting on fancy gadgets or extras.