Much of Dead Island's game engine appears unchanged in Dead Island Riptide.
What changes have been made to the game in the jump from Dead Island to Dead Island Riptide?
The difference is basically better graphics for a new game. The playing mechanics are the same and the story line is the same. Riptide adds a "fear factor" into the game with it's bonus scary sound effects.
There's also another difference in graphical terms
Riptide seems to look more vibrant/colorful While the first installment looks a bit dark and washed out