Mainly on offense. Their last years starting line played a sum total of 15 snaps together, most significant was Taylor Decker, their starting LT who missed 8 game and was replaced by the gawd awful Greg Robinson. Both 2017 FA additions Lang and Wagner were in and out of the lineup, and Swanson missed significant time with concussion issues. All the injuries had 10 different line combinations in 16 games, the most in the NFL. Swanson was replaced by Ragnow, the Lions first round draft pick and shoe in starter. They then added Blount, and drafted Kerryon Johnson in the second round, and already have one of the best 3rd down backs in the NFL in Riddick. This means their 2017 starting RB Abdullah is in danger of even making the team. They have a nice young WR in Kenny Galloday, now in his second year that is having an eye popping OTA's, and should give the Lions the best overall WR group in the North, and top five in the league.
Defense is still suspect, no one knows what to expect, or how Patricia will deploy them, but he does have a history of making players better. Anybody that can get serviceable play out of Shea McClellin or Kyle Van Noy has to be doing something right. Lions do have a solid secondary with anchors Slay and Quinn, defensively keys to success will be the growth of 2nd year player Jarrod Davis, and contract year Ziggy Ansah. They get back Zettle who was out all of 2017, and anything out of second year Cb Tabor will be a bonus.
I expect a top 8, maybe even 5 offense, with a slightly improved defense (coaching). Much of the improvements might be nullified by SOS, so I expect and 8-8 9-7 season, possibly 10-6.
Bears will be greatly improved too, but I expect much more growing pains, with a second year QB on his second offensive system. Bears are getting the pieces, but pass rush is suspect, and this is a division where you need to pressure the QB. They will show flashes of what they can be, but I don't see it coming together until 2019. And all this hinges on MT, who despite all the cute nicknames, is still very raw and unproven. I see anywhere from 6-10 to 8-8 for the Bears, but they will be much more entertaining to watch than the Fox bears, that is for sure.
At any rate, at this point, almost every team in the league can claim improvement, not just the Bears.