Without knowing what German games you played or what you games you are comparing them to it's tough to really provide a good answer for your question. I will be happy to tell you what I find enjoyable about "German" games, though.

First and foremost, I find that "German" games manage to pack a lot of interesting decisions into a short, generally simple set of rules. El Grande, for example, has a very simple set of rules. Those rules, though, result in a dynamic game with lots of interesting decision making. In my experience, most "American" games with simple rules are also simple games. To find "American" games with depth to them one must usually also be willing to wade through many pages of rules.

Second, the components in German style games are generally superior to American style games. Games are, among other things, a tactile experience. I find it more enjoyable to play a game with really nice "bits".

Elfenland and El Grande are examples (though hardly the only ones) of this. The pieces for the games are wooden rather than plastic and have a great feel to them. Another example, though not German (it's English), is Upstart's TheReally Nasty Horse Racing Game. The six horses provided with the game are large -- 2 inches long -- nicely detailed and hand painted. If the game had been made in the U.S. the horses would have been small, colored pieces of plastic. The game itself might not have been any different, but the experience would have been diminished. (In my mind, this difference is similar to the difference between watching a movie at a movie theater versus watching the same movie on a 19-inch television.)

Americans, for the most part, seem to be of the opinion that games are for children. "Adult" games are generally party games. If you're an adult who wants to play something other than party games or war games, you're pretty much out of luck. In Europe, though, games are viewed differently. The games produced there reflect this.