I would say pass rush and running game.
We couldn't run the ball effectively when we wanted to and most of the season our pass rush was MIA.
Now take into account our two best OLB's were missing in many games and we didn't have them both on the field at the same time till at the end.
We only had two or three games out of the entire season where our run game played well, other than that they wern't very good.
I would like a strong OLB,ILB, too but I believe we need more help on the offense beside RB. we also could use a good TE, WR, and o-line help.
I keep thinking of all the positions and the outcome of last season and it keeps coming up inability to score enough points , thats the problem folks, and its the main problem.
Look at the Ravens, their defense isn't as good like they use to be, but they did play excellent in the Pat game. They also gave up over 400 yrds, against the Colts but still won. The reason is their offense is coming together and Flacco is playing good.
We are going to duplicate this season unless we get this offense working to score more points.
You average 21 points a game and you will be sitting at home for years......GET THIS DAMN OFFENSE IMPROVED and FAST!