According to Wikipedia in a nutshell:
- guided non-linear gameplay ( a nonlinear game may permit multiple sequences to finish the game, a choice between paths to victory, different types of victory, or optional side-quests and subplots)
- a large interconnected world map the player can explore and progress in, although parts of the world will be inaccessible to the player until they acquire special items, tools, weapons, abilities, or knowledge within the game.
- acquiring such improvements ( special items, tools, weapons, abilities or knowledge) can also aid the player in defeating more difficult enemies and locating shortcuts and secret areas, and often includes retracing one's steps across the map.
- Through this, you need tighter integration of story and level design, careful design of levels and character controls to encourage exploration and experimentation, and a means for the player to become more invested in their player character through role-playing elements.
- Metroidvania games can be two-dimensional side-scrolling platform games, and also top-down and 3D games.
Hope it helps.