The longer they sit on the tree, the more flavor they have. Store bought tangerines always lick ass, because they have to ship them long before they are ready and then artificially ripen them. I grew up with a tangerine tree in my backyard and ate them by bucket full at perfect ripeness... Ignorance is bliss.
Usually when tangerines taste more watery than orangie, it's because they are probably picked too early then ripen on the way on the transfer trucks to the stores. So they don't fully mature naturally so to speak. Also, they could be really dry.