There are two things different about most LED bulbs:
1) They are usually longer than halogen bulbs. Most come with instructions on how to cut the dust caps & install rubber grommets that allow the wires to pass thru.
2) The LEDs are mounted sideways on the stalks & shine out sideways, using the reflections off the inside of the headlight bucket. An incandescent bulb shines primarily from all sides.
If one chooses a good color temperature LED bulb, the light is usually whiter & brighter. Many cheap LED bulbs have "shadows" present in their light beam. This comes from the positioning of the LED on the stalk. Better LEDs will have multiple diodes around the stalk or they will use a reflector to bounce the light back out to the front of the headlight instead of mostly to the side. We have seen drastic improvements in LEDs just in the last 5 yrs. I have all LED lights in my home. I'm sold on the technology as I saw a significant decrease in my electric bill & a big decrease in the amount of heat produced by the bulbs.