Since 2011, the Bengals have drafted really well and consistently found themselves in the playoffs every year as a result. 29 of the 45 they players drafted since 2011 are still with the team. That's not even counting players like Mohamed Sanu or Marvin Jones who are no longer with the team primarily because they were so good that they received huge contracts with other teams in free agency.
However, the Bengals have had their fair share of draft busts too. Of the 16 players drafted since 2011 who are no longer with the team, six aren't signed with an NFL team at all. Those players are Lavelle Westbrooks, Orson Charles, Jay Finley, Ryan Whalen, Dan Herron, and Robert Sands.
Sands, in particular, was recently rated as the Bengals' biggest draft mistake since 2011 by ESPN. It's a little bit of a strange designation for a player who was drafted in the fifth round, but it's true that his short lived career in the NFL was anything but encouraging.
He managed to find his way into the lineup once in his rookie season in Week 13 against the Pittsburgh Steelers and accomplished exactly nothing. He didn't see any more playing time for the rest of the season and found himself on injured reserve with a chest injury before the 2012 season even started. Pile on top of that a few counts of domestic abuse and his ex-wife accusing the Bengals of covering up his tendencies and you've got a player who was nothing but toxic to the entire franchise.
That said, as previously mentioned, he was only a fifth round draft pick. There have been a few other more significant busts since 2011. For example, ESPN notes both Russell Bodine and Margus Hunt as other players who haven't really lived up to what the Bengals expect.
Bodine has been a starter, but mostly because there isn't another center on the team who is going to make a difference. The Bengals gave up a pick to get him. They traded a fourth round pick (123) and a sixth round pick (199) to the Seattle Seahawks in exchange for the fourth round pick (111) that they used on him. He has generally been lackluster and inefficient as the team's starting center so far, so giving up a pick to get him seems pretty silly in hindsight.
Hunt, on the other hand, was a second round pick that the Bengals took in 2013 almost entirely for his physical potential. They knew that he would be a development project as the native Estonian only started playing football in 2011 because the sport he originally wanted to play was no longer carried by his college of choice (SMU). He was generally known as a physical freak coming out of college who, with the right development, could become an absolutely unstoppable machine at the NFL level. Unfortunately, he's only had a few opportunities to get onto the field so far and he hasn't performed particularly well, posting only 2.0 sacks and seven tackles in the regular season and playoffs. However, the main reason he might be considered a bust is the fact that he hasn't produced for the team despite being taken fairly early in the draft.
Another player who could be considered a fairly significant draft mistake is Dontay Moch. The Bengals picked Moch in the third round, 66th overall, in the 2011 draft. Like Sands, his career with the Bengals was marred by injuries and legal trouble. However, unlike Sands, the Bengals picked him up on Day 2 of the draft. Due to a broken foot in the preseason, he missed the first six weeks of his rookie season. He eventually returned to full practice, but never got in on any game action.
In his second season, he missed the first four games due to a substance abuse suspension. He only managed to play a single game after that, recording no stats, before finding his way onto the injured reserve list with recurring migraines. The Bengals released him at the end of the season and briefly brought him back in 2014. Once again, he failed to make an impact and was cut.