I think a somewhat simple rpg would be a good idea. Possibly something in the style of an older rpg. Maybe with fighting and puzzle/problem solving elements. It dosen't seem like it would be super hard to make and seems pretty achievable if the work or elements needed are split up.
Alternatively, if an rpg is too complex, an interactive fiction/choose your own adventure game may also be a good idea. It could have similar or most of the same elements but with a lot less work needed for visuals and without a need to figure out combat mechanics
I think it would be cool for it to take place in space or on another planet. The main character could wake up on another planet and be attempting to get home. They'd need to befriend and talk to aliens and convince them to help them or fight and threaten them to get their stuff if they're not too agreeable. Befriending and convincing could be done through offering services or trading items in order to gain the trust or help of others. In the end in order to get off the planet, they'd need to eventually fight someone for their ship or convince them to join their side. They may also need to avoid being killed by aliens who either want to eat humans or just hate humans (or are out to offend those the human threatened).
Either keyboard or mouse. Either would work for the purpose of this project since you would mostly be controlling where you walk to and what you choose while talking or in battle. If you wanted to make combat more interactive, you could make it so that you have to time presses/clicks or press certain keys in an order/ do certain actions with the mouse
Something cartoony or pixelated and pleasant to look at would likely be a good idea. Vibrantish colors could also look be nice to look at, and could fit with an alien world. I want to say animesque in character designs but that's not a great description. Maybe like semi-realistic propotions but obviously cartoony features?