The good, bad and ugly of the Bengals defense at quarter mark of season

The Bengals defense has had some issues through the first month of the season, but they've still been among the NFL's best units in many regards.

Thanks to the return of nearly the entire starting unit, not to mention several backups who started games last year, this is a defense that has the perfect balance of experience, chemistry, depth, and impact players at all three levels.

It starts up front with the entire defensive line of last year back for another tour of duty. Geno Atkins, Domata Peko, Michael Johnson, and Carlos Dunlap are once again among the league's best defensive lines.

At linebacker, Rey Maualuga and Vinny Rey have continued to play at a high level, while the addition of Karlos Dansby help offset the loss of Vontaze Burfict over the first three games of the season.

The secondary has a nice cornerback trio of Adam Jones, Dre Kirkpatrick and Darqueze Dennard that continue to show more and more promise every week. The safety tandem of George Iloka and Shawn Williams both strike fear into any receiver coming across the middle, though, there’s room for improvement.

Now, let's review how the unit has performed overall during the first four games.

The Good

Cincinnati has racked up nine sacks through four games, which is tied for the 12th-most of any NFL team. The frequent pressure the defensive line has produced is a big reason why Cincinnati is allowing the fourth-lowest completion percentage (57.6%) this season in addition to ranking 10th in pass defense.

Everyone knows Atkins is a big reason why as he's one of the game's best interior lineman. He's up to 11 tackles and 2.5 sacks through two games while ranking as Pro Football Focus' second-best interior defender. That includes all 4-3 and 3-4 interior defensive linemen.

Atkins has helped the Bengals to allow the 13th-lowest rushing yards per carry (3.8). Cincinnati is also one of two NFL teams (Detroit) to not allow a rushing score this season.

However, the man not getting enough credit for his impact is Carlos Dunlap, who has become one of the game's best defensive ends. He's done it all through the first four games with 18 tackles, three sacks, one forced fumble, and five pass deflections.

PFF ranks Dunlap as their No. 2 edge defender through the first four games of 2016. That includes defensive ends and 3-4 outside linebackers, and only Von Miller, the highest-paid defensive player in football, has a higher grade than Dunlap.

The linebackers deserve a lot of credit for this defense's success as well. They've rarely missed tackles and allowed running backs to get past the second level of the defense.

In fact, Cincinnati's longest run allowed this year is 16 yards, which is the second-lowest of any team. Having two physical safeties in Williams and Iloka has also aided this effort.

The Bad

As good as the defense has been on a down-to-down basis, they've had some serious mental lapses that have allowed too many big plays. Cincinnati has allowed 10 passing scores this season, which is tied with Cleveland for the third-most of any team.

The Bengals defense has also allowed 11 passing plays of 25-plus yards, which is tied with the Dolphins for the fourth-most of any team.

Scoring-wise, Cincinnati is allowing 20.5 points per game, which is the 13th-fewest of any team. That's up from 17.4 points per game in 2015. This defense is good enough to replicate what last year's unit did, but so far, they've allowed a field goal more per game.

The Ugly

The low point of the defensive struggles came in Week 3, when the Bengals allowed Trevor Siemian to torch them in his first career road start. Siemian was 23 of 35 for 312 yards with four touchdowns and no interceptions for a 132.1 passer rating.

He was 10 of 11 for 168 yards in the second half, including two scores that came after the Bengals took a 17-16 lead, but lost 29-17.

Siemian became the first player in NFL history to throw for over 300 yards with four touchdowns and no interceptions in his first career road start.

Going Forward

The majority of the Bengals' issues thus far has been very correctable. Getting the wrong defensive signal, not knowing an assignment, and poor technique on a handful of plays has allowed offenses to capitalize with big plays.

We saw similar issues plague Cincinnati last year, but they improved as the season wore on and became the driving force of this team down the stretch.

This unit has the potential to do the same as along as everyone stays healthy, especially now that Burfict is back and getting re-acclimated to his starting spot.