It is star players going on scrubs but once you're familiar with the college game, you can tell the guys who will go on to be productive in the NBA.
For example, you could tell Austin Rivers wasn't ready for the NBA and wouldn't have that much success. You look at a guy like Kyrie or Unibrow, everyone knew they would be productive NBA players.
Then you have cases like Drummond. He was pretty lackluster in college, but has been GREAT in the pros. So you just never know. Your best bet is to just watch college basketball during March Madness, you'll see most of the top draft prospects play then.