Of course you CAN, that's not a question of the engine but a question of the grafics you use in first case...

Of course the engine is also important, but with the GS you can achieve good results if you want to. But you have to keep in mind, that there wasn't only one person working on games like riven or syberia...

To achieve those results you would need very high quality textures and good knowledge of programming and a LOT of time if you want to do it alone.

EDIT: I don't want to say: 'What you want to do is impossible in gerneral'.
I would be very happy for a new classical adventure game, but keep in mind that taking riven as model for your game is like taking oblivion as model for an rpg.