Yes, you seem to be underestimating how advanced Crysis is. There is NO other computer game invented that puts more workload on your system components. As Latios has said, the top notch PCs of today, with adjusted everything from FSB speed to CAS Latency, come to a grinding halt when faced with something a bit graphics intensive that Crysis throws at it. In fact, Crysis is a benchmark nowadays - if you can play Crysis smoothly, you can play ANY other game. And I guarantee it, you won't be able to play Crysis acceptably with any brand name computer.
And also, if you didn't understand what Latios was saying about the dual-core processors thing, try this.
Think of each core as a truck which carries information. The speed that the truck goes is the clock speed of your CPU. If you have two trucks (or cores) going along at 100km/h, that doesn't mean the total speed is 200km/h. It just means that in theory you can transport twice as much information in the same amount of time (but not the other way around, ie. a piece of information in half the time).
However, some games and other programs require your truck (or core) to have a faster top speed. It doesn't matter whether you have 1, 2, 4, or 8 cores - if your trucks aren't getting there fast enough then it just won't happen.
With that in mind, you should also realise that at the moment quad-core processors are overrated. In terms of real-life usage, you will never optimally utilize all four cores efficiently. Especially given that the clock speeds of quad-cores are lower than dual-cores of the same price, you would be wasting your money purchasing such a processor in the hopes of getting amazing performance from a single application.
You're much better off getting a dual-core with a high clock speed until multithreaded applications become mainstream.