of course the gameplay is going to stay the same. after all, "why fix it if it isn't broken". if the gameplay is good and they make another, of course it's going to feel the same. the only difference is the games story and that's why you play it. you play games for the fun, the story, and/or if your a multiplayer fanatic you play online only. if you like the first game enough, you buy the second sequel to the game and enjoy that why? because it's different.
and Soul Reaver? they never made a new Soul Reaver since Legacy of Kain: Defiance which was released around the 2004-2005 era.
Have you even played the first mafia? the first mafia revolutionized the sandboxing/gta style of gameplay. go over the speed limit - get a ticket. run a red light - ticket. cops find a weapon on you - jail. point is, it was a different game.