The Top 5 rating was a bit contrived. It was greatly helped by taking 32 commits. Probably didn't hurt that Callahan was good buddies with one of the big-wigs at Rivals as well. Looking at the 247 Composite, it didn't have any more 4/5 stars than Pelini had in the middle of his time here. Plus the averages star rating was less, though that is tougher to maintain with more recruits. And it wasn't like that class produced a bunch of four-star studs - there were plenty of busts (just like most classes) with Rodney Picou, Chris Brooks and Harrison Beck not exactly turning into household names.
That being said, the class did have some headliners. Marlon Lucky was a consensus five-star. Rivals also had Zach Bowman as a five-star (though he was gone by the time Pelini got here). And Suh was obviously the stud of the class as a high-four-star.
But as to
@Hedley Lamarr's claim that the 2005 class resulted in one of the best defenses in the country, I don't think that's really the case. Suh and Dillard were the two leading tacklers. Turner was a very solid starter. But those were the only three left from the 2005 class by the time 2009 rolled around. The other defenders in the class were mostly gone by 2009 - Potter, Bowman, Glenn, Dagunduro, Cryer - or non-contributors.