Pushing against the pedals can tire your legs, which is less comfortable than walking on a treadmill. This does not mean that the treadmill is better; on the contrary the elliptical is complete! Your legs will need some time to adapt before it done. But this will allow you to burn many calories and is an excellent exercise to lose weight.
If you want to do the exercise to lose weight, you have to have fun doing it. If you exercise to lose weight too violent, you become discouraged very quickly and you will not reach your goal.