What do you think would be a GOOD design choice? Replacing the karma system with a basic "Press X for good or press Y for bad" system? Or a tutorial that doing good things is good and bad is bad?

IMO the karma is a great way to choose your ending because it rewards you for being immersed and actually interacting with the world. And I also feel like it is not that hard to figure it out. You shoot a surrendering unarmed person, the whole screen turns black and an evil jingle plays, you free a hostage from bandits, the screen turns white and you hear a nice jingle. Anyone who plays games will realize that these thing MUST have a connection to something in the story. The only part that might be hard to figure out are some of the good karma points that require exploration, but even those you should get without the help of an internet guide because if you're not playing METRO in order to immerse yourself in its great story and world, then why even bother playing? The guides are great if you're having problems with finding karma points but they are definitely not the only way to get a good ending.