The idea that, "God wants us to be happy," is the basis for a lot of bad theology in our day and age.
Happiness is elusive... even in supremely comfortable, desirable, and wonderful situations, many people will not "feel" happy... and even in supremely difficult situations, some people choose to be content and pleasant and might even feel happy.
While I'm sure God doesn't mind in the least if we're happy, I don't believe His main "want" is for our own happiness-- rather, it is-- primarily-- for His own glory and, secondarily, for our good. His glory and our good do not always add up to us being happy... they may at times, and they may not at other times. Particularly if our feelings of "happiness" depend on being able to have our own way, which they often do.
If God just wants us to be happy, then He sure has unnecessarily burdened many people with sadness and suffering and certain unhappiness, including Joseph, Hosea, Paul, Hagar, Leah, and Stephen (and me! can I make the list?), but above all-- Christ Himself . Happiness, I daresay, was not the ultimate aim there. Nor is it, I'd put forward, His aim for us today.
Joy may indeed be a derived and intended result from His will for us... but instead of joy through feelings of happiness, it may at times be joy through contentment: in pain, hardship, and sharing in the sufferings of Christ. Considering all of this, while I'm confident that God offers immeasurable joy to His children, we need to beware any theology based on shaky sentences like, "God wants us to be happy".