Misty Step is a level two conjuration spell that lets you teleport anywhere within 30 ft. of you as long as you can see the unoccupied destination. On the other hand, Dimension Door is a level four conjuration spell that lets you teleport anywhere within 500 ft. Dimension Door also lets you bring with you someone else, which Misty Step cannot do. Overall, Dimension Door is a much more powerful spell and that is obvious given the difference in levels.