I don't think an elliptical counts as running, it's sort of a machine. Kind of like a Gazelle. Unless you mean an incline treadmill or something...
I guess it's the closest thing to walking/running short of running though It's good how it's easy on the joints, I like that.
Don't criticize machines for 'working you out'. Ellipticals are just fine, the main goal of cardio is to elevate your heart rate and stress your vascular system. This can be done with anything. Something is only bad if it causes injury.
Of course, running should be done too, but mainly to become faster and a more efficient and less injurious runner. You can push your cardio levels with it too, of course, and the impact you experience in it probably takes more strength, but I don't see a problem in doing that separate from cardio machines. If anything, I'd think exhaustion would deviate from your form, sprinting for short HIIT periods seems better.