The project has moved here by the way:
https://github.com/KrossX/Pokopom
He states in the README that Linux doesn't have a GUI yet (although I'm not sure why, I thought it did at one point). So that part isn't your fault.
What I think might be happening is you are experiencing games which need to be fixed somehow. With Castlevania Chronicles (the game I used for testing), performance was good with Pokopom. I have a feeling you just picked games that run slowly at the moment.
https://github.com/KrossX/Pokopom
He states in the README that Linux doesn't have a GUI yet (although I'm not sure why, I thought it did at one point). So that part isn't your fault.
What I think might be happening is you are experiencing games which need to be fixed somehow. With Castlevania Chronicles (the game I used for testing), performance was good with Pokopom. I have a feeling you just picked games that run slowly at the moment.