The experience of using legal stuffs from the OS to the apps was alone satisfying for me to completely transfer to linux.After I got used to it and the features it provided,usage of the OS had become indispensable to me.But still then i had been going to XP occasionally to play some games.
The bad parts about Ubuntu that i found was :
1) Lack of OpenGL based games and onyl for windows.
2) Audio driver (realtek) was not properly implemented i think.Was not able to use headphones and dint have audio configurations.
The best parts are that
1) Both the OS and the apps are completely FREE
2) Great user interface transitions and easy usability.(I still hate to learn those command line interface though i know it has some advantages too)