If you want a semirealistic planetary classification system, here's a proposal.
Silicate planets, composed mostly of silicate rocks with an iron core and little water on the surface. In an ideal distance, they have liquid surface water ("Earth-like planet", "garden planet" or whatever). Further away from the star, the surface water is frozen ("cold desert planet", like Mars). Closer to the star, where it's too hot for liquid water to exist, you'll have "greenhouse planets" (Venus), and even closer, "hot desert planets" (Mercury) where the atmosphere has been boiled away. And right next to the star where the surface is hot enough to stay partially molten, you have "volcanic planets".
Water planets, composed of about 50% water and 50% heavier elements. In a distance where liquid surface water may exist, they're "ocean planets" with no surface land and a 200km+ worldwide ocean (Gliese 581d is one possible example). Further away, they're "ice planets" (like most of the larger moons of Saturn and Jupiter) with a subsurface ocean or thoroughly frozen if cold enough. Close to the star, they "steam planets" or "sauna planets" with an atmosphere composed mostly of water vapour (I shit you not, these things have been hypothesized).
As you can see, every important planet class is covered this way. If you want more exotic terrestrial planets, add carbon planets (with a global layer of diamond kilometers thick) and iron planets composed of heavy metals.
You could divide giants into "gas giants" (Jupiter, Saturn) and cold, bluish "ice giants" (Neptune, Uranus) and then use the Sudarsky gas giant classification for added realism, which gives the possibility of SPACE WHALES FLYING IN CLOUDS OF IRON. Fuck yeah!
Oh, and don't forget asteroid belts.