As much as people want to bag on Marshall when things go poorly for him, it's not on him Chicago missed the playoffs. They were still a 10 win team. That being said, Chicago has glaring weaknesses.
That OL is comical. Outside of drafting Gabe Carimi in the first round in 2011, they never made a serious push to improve the OL since drafting Chris Williams in 2008. Now I'm not saying take our approach of multiple early round OLs, but you gotta make some effort in improving that.
Outside of Marshall they just don't have any weapons in the receiving game except Matt Forte on swing passes. Alshon Jefferies did not have the impact they were expecting out of him (some of that was injuries), Devin Hester has been fairly useless at WR, Johnny Knox missed the year recovering from a broken back, and they have no consistency at TE (and they can thank Mike Martz for that).
I respect Chicago's ability to get the most out of any and all defensive players they have (Ask Colt fans what they thought of Tim Jennings while he was in Indy) but they are not good at building an offense.