L4D is an older game, so one might expect in terms of gameplay, size (as in playable area) and stuff of Dead Island might be bigger.
Also there's something called "horror concept" or something of that effect. There are different kinds of horror. There is the psychological horror, like Silent Hill; there are the visual horror, like Resident Evil (specially the most recent ones); the zombie-horde like Dead Rising and so on. All I know is everyone I know who played L4D loved it, it's a real survivor horror. And many people just LOVE Dead Space even more. But never heard any hands-on about Dead Island but the trailers and concepts looks like pretty sweet