|Screenshot from the jMonkeyEngine.com homepage.|
It requires quite a bit more programming work than the BGE, but it also has more possibilities because of it. It's currently in beta, but people have used it to make quite a few impressive games with it, as you can see here.
It has many features, including a built-in terrain editor and a fairly advanced water shader. It's quite impressive, really.
Download the SDK for free from the jMonkeyEngine homepage here.