It will mostly depend on the game and its genre but to me a good game generally needs variety in how it uses its game mechanics so it doesn't become too repetitive. It also having game mechanics that are unique to it or how it uses those mechanics in a different way is needed so the game can feel unique from things I have already played. However if the game lacks these components it really needs to have a interesting world/characters/story and a good atmosphere to make me want to play it.
Games that have exploration can be really fun in having choice in how and where you want to go about areas but I prefer them to not be fully open world so it doesn't feel empty. Game that have choice in what strategy and items you can use can be interesting and increase replay value and variety in gameplay but the different things you can use need to feel unique from each other and not have too many of the same stuff so it doesn't feel like there are a bunch of meaningless options. More linear games without much choice can be just as fun as the developer has more control over the experience and so its more able to be refined better.
I can particular like very difficult games as I like completing hard challenges but without much punishment for failure which these games will provide as if I fail. Its not like I am not going to become bankrupt or lose someone close to me so that makes failure in these games fun.
A beautiful or unique visual aesthetic and great soundtrack are of course good bonuses to a game that can make them shine even higher but not completely necessary.
I will mention some games that I think are really good in these aspects:
- A Hat in Time - most fun I had exploring a world in with its movement with charming and fun characters to interact with.
- Rain World - unfair in its difficult but that just boosts the experience of the game to make it feel like you are surviving in the wild against the predators that want to eat you and the harsh environments you have to move across sometimes and get lost in.
- Baba is You - very difficult puzzle game with mind blowing game mechanics in how you solve each level and even later into the game with how you move in the world map.
- Dark Souls - while I am a bit bored of souls-likes now, this game was enjoyable for its difficulty, harsh atmosphere and choice in what you use against enemy encounters.
- Omori and OFF - RPGs with interesting and compelling stories/world, immersive and sometimes tense atmospheres which are enough for me to still love dearly them despite some repetition with their combat systems.
