The new Ford GT is radically different from the modern classic it replaces. The obvious difference is the engine: The last generation had an old fashioned V8, where the new car follows Ford's trend of turbo V6s. The personality of the cars couldn't be more different as well. The last model was an homage to the race car of the 60's, with the centerpiece being the massive engine, beautiful styling, and analog sensations of the manual shifter and lack of traction or stability control.
On the other hand, with a 600hp V6, dual clutch transmission and aerodynamics taking precedence over being pretty, the new GT is a race car first and a road car second. The car goes 0-60 in under 3 seconds and has a top speed of 216 mph. Ford used higher quality materials than its predecessor and Demuro describes it as not cheap, but basic. The brand new new Le-Mans ready Ford GT is rumored to cost around a half million dollars.
All you really need to know about the differences between the two? An owner of the previous generation sees no problem with owning both as they are different enough to where the intended uses don't overlap enough to make the old one outdated. It is rare that two cars that share a name can be so different. But it means, at least, that the old one we know and love has not been truly replaced.