here is a full example of an asteroids game:
Originally post about it:
…the googlecode links are broken but they were moved to the github link at the top.
This example uses an Entity System.
That’s going to be the problem with any real game is that it’s bound to have some additional add on code to make it work. JME is lower level than that… which is flexible… but you will likely add stuff to make a game (or use additional libraries). (I highly recommend Lemur, Zay-ES, SiO2, etc… but then I would because I wrote them. A lot of people use them, too, I guess.)
If you don’t want to use an ES then there are other game examples out there. Just search the forum.
Edit: note that there were also two books published on JME.