I am getting near releasing my game, and the game's trailer is important to sell the game.

I was told the game needs to show what the game is like, but I think it also needs to appeal to the person viewing the video.

I think this trailer achieve the first, but not the latter… I got an advice to show something really epic, like maybe getting near to a boss fight… how can I improve this trailer?

For context, this is the store page:

https://store.steampowered.com/app/1292410/Golden_Fall_2/

Well your trailer shows the combat, vendor system, lever to open doors, character creation… Depending on what else cool features you've got in your game, you could add them, like boss battles as you mentioned. Other than that the trailer seems well made.