Peyton Manning. First overall pick in I believe 1998. Everyone knew he would be great.
Some doubted his arm strength but that was more because of the comparison to Ryan Leaf.
Predicting if a team had a good draft is very much a guess. Predicting if a team had a bad draft is a lot more firm.
From just an anecdotal observation, teams seem to do better when they have lots of draft picks rather than trading up and having only couple. Picking up a lot of guys in the 2nd, 3rd and 4th rounds really seems to be the way to go to build a solid team. Dallas during the 90s, Tampa Bay in the late 90s and the present day Eagles seem to do a really good job with this approach.
The Falcons on the other hand have a history of trading away their 2nd and 3rd round picks just to move up a few spots.