Although some things have been already mentioned, I put here my spare comments:
Main Menu: The menu has too less contrast, the white text on pastell-bright green/blue background makes reading too hard. Although I like the gradient of the background, I somehow dislike the buttons and the colors scheme of the upper menu bar. The overal design of the menu isn't convincing as well. For a debug screen its okay, but a _game_ menu should be more scattered and friendly to the user.
Loading process: You should add a "loading / connecting in progress" bitmap or such. Plus, the camera is misplaced in the very first frames of the map. You should turn off the loading screen when the loading has finished and the map reset/initialization has been finished (camera, etc.).
Ball movement: I guess you do the physics calculations on the other's client side. So, all receiving clients get "stuttered" ball data and therefore you should interpolate the ball movement/rotation on the receiver's side to make it smooth.
User presentation: I like the way you can interact with the shortcut voices. You could also take benefit off users with their own custom ball colors. In addition, you should add a golfclub to visualize the power and direction of the ball hit (again with the user color). User avatar pictures combined with "on-the-fly" rankings would make it more attracting.
Game tactics: In real life, everyone finishes his course and then the other is able to play his round. The benefit of a virtual - and online! - minigolf game would be to make the whole game roundbased: player 1 makes a hit, then the other one and so on. This brings in a competitive gameelement. Imagine 4 players are playing and the three others have to wait until the course is finished. Also, a notice about the common amount of hits for finishing the course (par) would be motivating as well.
Leveldesign: I like, that you tried to make a realistic minigolf parcour, but it is somehow boring. I know a lot of _funny!_ mingolf places with windmills and all thos funny stuff. YOu use very much concrete, cobbles and stone here, which makes everything "cold" to the user. Plus, although you did a good job on the shadowmaps, the whole map is WAY too dark. Its maybe a night scene, but its too dark and for my taste - a disgusting place. I guess that not too much children would like to spend their time there (real life children and virtual ones as well
). I am sure, that you made the clear decision for a realistic map, but you should kick your graphics/texture designer to make something better that attracts people.
