Creating a 2D game with Unity

There are many 2D games that are on the market, but only a few stand out to me.  Some of these are: Geometry Dash , Mario  and Candy Crush .  These games have been very successful and have been popular throughout their time.

Play style and Artwork  

However, they all play differently and have have different art styles which make them unique.  For example, Geometry Dash is a harder plat former that is based on reaction time and remembering the level to complete it (reaching the end).  Mario has a similar concept but it plays differently as the user gets to play at their own pace and the game has a different art style.  Candy crush has a complete different art style and end goal.

What I want to do 

I want to create a 2D platform where the goal it to eliminate all the enemies on the level to complete it.  The user can choose their weapon at the start of the level and has to avoid being killed by the AI.