Has Jim Caldwell under or over achieved? Well, let's look at the body of work.
2014
First off, let's recognize how sorry the history of this franchise has been. 11-5 might be a ho hum season if you're New England, Pittsburgh, or Green Bay, but around here it's exceedingly rare: 1962, 1991, and 2014. Signature win: week 3 over the Packers at Ford Field. Embarrassing loss: 14-17 at home to the Bills two weeks later, who carried former Lions HC Jim Swartz (DC) off the field. Won all the games they should have: swept the Bears & Vikings, beat the other mediocre/lousy AFC East teams, beat a bad Saints team at home, squeaked by a mediocre Falcons team on the road. When they faced tough playoff caliber teams, they predictably lost, and it usually wasn't close: @ CAR, @ ARI, @ NE, and @ GB to end the season with the NFC North crown on the line. In the WC Playoff Round, blew a 13 point lead - largest blown lead in franchise history for a playoff game. Give them credit for taking care of business versus bad teams, but at no point did it seem like they were capable of a deep run. There are deep psychological issues to this franchise that seems to transcend who the current coach or players may be; put another way, same old Lions. 11-5, first round exit
2015
Faced with a challenging schedule to begin the season, the Lions folded. Things started promising: early in the road opener at San Diego, Ameer Abdullah took his first NFL touch 24 yards for a TD. The Lions blew an 18 point lead - the third biggest blown lead in their 82 year history in Detroit. Following that came a 10 point loss @ MIN, a 12 point loss to DEN (Slay gave up a horrible long TD to D Thomas late in the first half), and then the MNF batted ball debacle at Seattle. They lost their will after that: 17-42 blowout to ARI at home, barely won in OT v. the Bears, Vikings completed their sweep. On the way to London to play the Chiefs they fired OC Joe Lombardi, the O-line coach, and the strength & conditioning coach. After a 10-45 embarrassment and a bye week, Jim Bob Cooter started to simplify the offense. They won in Lambeau 18-16 for the first time in 24 years, starting a 3 game win streak. A week after Thanksgiving they blew a 23-3 lead at home versus the Packers in the phantom face mask / hail mary game (with Ansah helplessly guarding the sidelines, rushing 3 and not enough men deep because they thought GB would run a second straight Stanford band lateral scramble.) After losing @ STL to Jeff Fisher, they won three meaningless games against losing teams. 7-9, missed the playoffs
Megatron retires (MJJ signs? not quite an equivalency eh)
2016
After starting 1-3, Darius Slay single handedly took over the game in the closing minutes with a forced fumble and interception to steal a win in Philadelphia. What followed was an amazing series of comeback wins, marred only by a flat performance loss at HOU as they won 8 of 9. Those early games foreshadowed what a fragile team it was: they blew a 14-0 lead in Indy, winning 39-35 when Stafford engineered a 3-play, 33 second drive that led to a Prater FG (safety on the last play of the game.) They led the Titans 12-0 and somehow lost 15-16. They were down 31-3 at Green Bay in the first half before coming back to make the final score 27-34. They lost in Chicago 14-17 when the offense failed to score a TD. They actually led the Eagles 21-10 at the half before - in a familiar pattern of the Caldwell/JBC era - they turtled up in the second half. The Eagles were trying to run out the clock when Big Play forced a Matthews fumble, and he sealed it with an interception after Prater put them ahead. After a comeback win at home versus the Rams, the Lions blew a 13-3 lead versus the Redskins. With 1:05 to play, Stafford took them 75 yards in 6 plays. Two weeks later @ MIN, Stafford got the ball back with 23 seconds and no time outs, but somehow got two completions to setup a 58 yarder by Prater. Tate's 28 yard in OT won the game. By the time they beat the Vikings on Thanksgiving, they had set NFL records by trailing 11 straight games, having 11 straight games decided by 7 points or less, and posted 7 comeback wins. After an easy win @ NO, they posted their 8th comeback win of the season versus the Bears. They gave up less than 20 or fewer points 8 straight games, the longest streak since 1961. Stafford tore a ligament in his throwing hand @ CHI. The Lions lost their last 3 games (@ NYG, @ DAL on MNF, GB on SNF) and got blown out in the playoffs. The entire season is summed up by Prater being clutch and Stafford in the first 12 games: 3,224 Yards, 21 TDs, 5 INTs, 67.5 Comp. Percentage, 101.5 QB Rating. In the last 4 while playing hurt: 1,103 Yards, 3 TDs, 5 INTs, 60.4 Comp. Percentage, 74 QB Rating. 9-7, first round exit
2017
Rather than go blow by blow, let's summarize this season by looking back at the season with 20-20 hindsight of knowing which teams are bad and which teams are playoff caliber:
- ARI, @ NYG, @ GB (no Rodgers), CLE, @ CHI, @ TB, CHI, @ CIN - give them credit, when they should have won, they did. 7-1 in these games, only lost in the lackluster Week 16 against the Bengals.
- versus playoff-bound teams: other than the great defensive effort in the 14-7 win @ MIN, they lost every time. They lost close ones (heartbreaker to ATL, the not-as-close-as-the-score @ CAR, the weird blowout to the Saints, the SNF coming out for JuJu PIT game, Thanksgiving Day versus the division champs, the blowout to the Ravens - pretty much every time they had a chance to make a statement, they failed. 1-6 against good teams.
Give Coach Caldwell full credit for a very good first season; on a historical basis relative to the Lions modest history, one of the most successful seasons ever.
Year two was a disaster. While they went 6-2 in the second half, what lingered is two of the four biggest blown leads in franchise history. He also gets credit for the biggest blown lead in team playoff history.
Year three was an amazing season of overachievement. Was that the result of coaching? IDK, I tend to think the bulk of that is Stafford being amazing in the last 4 minutes, and Prater being nails when they need him to be. I give Caldwell full credit for the blown leads: @ IND, TEN, PHI, WAS. It was a fun year, but they ended with four straight losses to good but hardly great teams.
Year four: what I'll remember most is how often they were unprepared at the start of games. I think it was 3 or 4 straight games they were down 0-10 before they finally unshackled Stafford. The playcalling was utterly predictable. No team had less success on first down, and their short yardage offense was pathetic. Stafford played great at times, but he got pounded all year. Lost an uncharacteristically high number of fumbles on strip sacks. The defense's emphasis on turnovers led to 5 TDs and Agnew took back 2 PRs, somewhat masking how poorly the offense achieved most weeks. The O-line had lots of injuries (as did the D-line before the season began), but so did the Ravens and they're headed to the playoffs. Injuries are not the whole story with the line play; to me, and I could be wrong, it feels like every week we are at a schematic disadvantage. How can you get beat by a career Y TE who has never had a 100 yard game going 5-175? By completely selling out to the run. How do you give up 200+ yards to the Bears and the Browns back to back weeks (& still win

)? Who gets beat by the Ravens play-action - only Detroit.
TL: DR
We should hire a new HC.