Large Dobsonians can show the Moon as a full disk, or zoom in to see lots of fine detail and many craters and other lunar features. They can see surface features on the planets, and they can easily show you Jupiter's moons and Saturn's rings, and you can see countless deep-sky-objects, including galaxies, nebulae, and star clusters. However, galaxies and nebulae will look gray and dim in any telescope, so don't expect Hubble-type views.