There is no set-in-stone definition of what "8-bit games" or "16-bit games" really means, so the answer to your question depends on your definition. See this related question.
- You can define them by the year they were released, which makes identifying which game belongs to which group is easy.
- You can define them by the color-range they use - meaning, you actually care about "8-bit-graphics" or "16-bit-graphics". In this case you basically need to count how many colors they use. 256 is 8-bit, 65k is 16-bit, etc. See Wikipedia's article on color depth.
- You can define them by the platform on which they were originally intended to run. This means you need to check the platform details. Early x86 games (such as most DOS games) are typically 16-bit, while N64 games are 64-bit. Many games are released to multiple platforms, though, which makes this tricky.
- If you define them by their gameplay, this is entirely up to you :)
In my experience, nowadays "8-bit" or "16-bit" usually refers to either the era in which the game was released, or its gameplay.