Eurogamer give Dead Island 6/10, Joystiq gives it 3/5. All reviews say it has bad coding, lots of escort missions (which I hate) and a ton of glitches but it's fun to play.
Funny, I've read most of the reviews and I didn't see anything about bad coding or too many escort missions. I have heard of a few glitches, mostly NPCs getting stuck or items disappearing with zombies (like if you throw a knife into a zombie and the knife disappears with the zombie). Most of those bugs should be fixed with a day 1 patch though. At least the AI glitches.
Most reviews seem to be positive with an average of about 7.6 / 10. The PS3 version seems to get worse reviews than the other versions.
That said, Deus Ex and Dead Island are two very different games. I'd say that Dead Island offers more gameplay hours since it has drop in coop and it's open world, but I haven't played it yet so I'm not sure. One reviewer played it for 40 hours before writing the review and he said he wasn't done with it. Deus Ex is a better single player experience for sure but I can't imagine it having a high replay value.
If you have 3 friends who are willing to play with you then I would recommend Dead Island but if you're just looking for a single player game with a fantastic storyline then go for Deus Ex.