Considering buying this game. I read that if you achieve a win condition, you get some sort of reward like a nice item and then start up a new world. Does that just go on forever? Or is there a real ending?

There is no real story ending. There are special event bosses, rivals, archenemies and such and you can win the region, but there is no point when the game itself ends. To make it simple it is a Diablo 2 that makes the road more important than the goal.