hmmm well lets see, in the 7th they take out a LOT of the old characters, like they dont have rider, oshare bones, Yu & Rei, ocean prince, Accord, Baldanders, and so on. In 15th anniversary theres a lot of special game modes, like spinner, giant puyo, underwater, ice block battles, and searchlight. Also Endless Fever battles. In 7th theres not a lot, except for great transformation (Daihenshin) which lets you turn into an adult or a child, being an adult makes your puyos bigger with stronger attack, being a child makes the puyos smaller with less attack, btu theyre set up in chains like fever mode.