World-class LinkedIn profiles have a few things going for them:
1) They are absurdly clear. In other words their summary clearly says who they are, and the rest of the profile supports that claim. For instance their summary might say they're a sales & marketing professional, the vast majority of their profile should relate to their ability to do sales & marketing -- otherwise viewers get distracted and aren't sure what you stand for.
2) They have professional-grade photos. While the photo doesn't have to be Hollywood headshot quality, it does have to look professional.
3) They include just the right amount of detail. LinkedIn profiles should be short enough to skim, but long enough to be interesting. You don't want someone turned off by the length of your profile, but you also don't want it so short that it misses the relevant facts.