So, got it today and played it for half a day now and I'm utterly disappointed. Sure, after some practice it clicks and you know what to do and how to win, but it's just not intuitive.
And that's the big thing I expected from Motion Plus games, to be intuitive and transfer motions you know from real sports 1:1 into the game. In GST, you have motion controls, but you have to swing the Wiimote the way the game wants you to and not the way you would do it on the tennis court. Also, it's not 1:1 but has some delay.
Additionally, it sometimes just does not do what you wanted and your player hits early. Does not happen that often after some hours of practice, but it should NEVER happen, because it totally kills the fun and it absolutely kills the outlook of having instant-fun multiplayer matches with your friends due to the imprecise controls and slow learning curve.
Let's see next week how Virtua Tennis implemented M+ and it looks like Sports Resort is a much better example of what M+ can do. Really looking forward to table tennis. GST just isn't the revolution one was hoping for but rather an updated version of Top Spin Wii with all it's faults.
