The 2014 season wasn't a great one for the Vikings -- they went 7-9 and finished third in the NFC North -- but it marked significant improvement and brought optimism that new head coach Mike Zimmer and rookie quarterback Teddy Bridgewater could be building a bright future for the franchise.

They shook things up in the offseason, losing a few starters in offensive linemen Charlie Johnson and Vlad Ducasse, linebacker Jasper Brinkley, and wide receiver Greg Jennings.

A concentrated effort was made to shore up what was a fairly weak defense. At cornerback, they added Terence Newman in free agency, spent their first-round pick on Trae Waynes, and stayed on the defensive side of the ball with their second-round pick, selecting linebacker Eric Kendricks.

Mike Wallace was brought in to replace Jennings at receiver, while Adrian Peterson looked to step right back into his role as the focal point of the offense after being suspended and missing almost all of the 2014 season.

2015 saw major improvements for the Vikings, and they finished the season 11-5, winning the NFC North, only to be knocked out of the playoffs when Blair Walsh missed a chip-shot field goal that would've won the game and sent the Vikings to the next round.

Let's take a closer look at how the season unfolded and what the future may hold for Minnesota.

The Good

Using our Net Expected Points (NEP) metric (which you can read more about in our glossary), the Vikings improved in virtually every area last season.

They moved from 28th to 20th in schedule-adjusted Passing NEP per play and maintained their 3rd-place ranking in Adjusted Rushing NEP. Their offense as a whole went from 25th to 11th.

There were similar improvements on defense, with their passing defense going from 18th to 11th, their rushing defense taking a big jump from 28th to 17th, and their overall ranking going from 21st to 13th.

While there was some concern when Peterson ran for only 31 yards in Week 1, he returned to top form quickly and led the NFL in rushing attempts, yards, and touchdowns on the season. His rushing success wasn't all volume-driven either, as his 0.01 Rushing NEP per carry ranked 21st among the 72 backs to see at least 50 carries this season. Jerick McKinnon also looked excellent in his complementary role, ranking third in Rushing NEP per carry.

Mike Wallace didn't step in and play a big role, but rookie receiver Stefon Diggs, a fifth-round draft pick, came on strong, making his debut in Week 4 and putting up 52 receptions for 720 yards and 4 touchdowns on the season. His efficiency was fairly solid as well, and among the 86 receivers to record 50-plus targets in 2015, he ranked 38th with a 0.72 Reception NEP per target.

There were a lot of bright spots on the other side of the ball too, leading to that big jump in defensive performance.

The pass rush, led by Everson Griffen and his 10.5 sacks, was among the best in the league. They ranked ninth, recording a sack every 14.0 opposing drop backs.

Eric Kendricks stepped in and made in immediate impact at middle linebacker, leading the team by a significant margin with 72 tackles and also recording 4.0 sacks.

Terence Newman proved himself to be an incredibly valuable signing and played a huge role in the Vikings' improved pass defense. He led the team with 3 interceptions and 12 pass defenses, while also adding 52 tackles.

The Bad

Despite the improvements last season, there are still major question marks surrounding the Minnesota offense.

At 31 years old, Adrian Peterson is almost ancient for a running back. His Rushing NEP per carry was well below his career average of 0.03, and while he has shown time and time again that he can defy the odds, nobody in the NFL is immune to aging. With the huge workloads he regularly sees, we can expect his production to decline sooner rather than later.

Bridgewater's 2015 season also created some room for concern. While he recorded 50 more drop backs in 2015 than 2014, his total Passing NEP was actually lower, and on a per-drop back basis, he fell from 0.05 to 0.04. He also saw his Success Rate (the percentage of passes on which he generated a positive NEP) fall from 46.3 percent to 42.4 percent.

His receiving corps also remains largely devoid of talent. Diggs' emergence was a pleasant surprise, but following a promising rookie season, Charles Johnson completely fell off the map, seeing only 13 targets in 2015. Mike Wallace, who wasn't particularly effective either, has already left and signed with the Baltimore Ravens, and Jarius Wright put up the worst Reception NEP per target of his career, a 0.64 that ranked 61st in the league.

Not helping out Bridgewater or his receivers at all was an offensive line that really struggled in pass protection. The Vikings allowed a sack every 11.1 drop backs, which was the second-worst mark in the league. While part of this can be attributed to the fact that they were the third-most run-heavy team in the league (meaning a higher percentage of their drop backs were coming on "obvious" passing downs), the number is still really concerning, and that kind of protection isn't going to help Bridgewater's performance.

Although the defense made huge strides, the Vikings still ranked in the bottom half of the league against the run, and the front-seven is still an area where they need to improve their personnel.

Looking Ahead

The next season or two are going to be incredibly important for the Vikings' long-term success. They have a lot of continuity in their coaching staff, returning their head coach and offensive and defensive coordinators for the third straight season, they have a young, promising quarterback who has proven to, at the very least, be a serviceable game manager, and they have a top-half defense.

In 2015, however, they leaned incredibly heavily on Peterson, and they're not going to have that luxury for much longer. While McKinnon is very promising, he will never be the generational talent that Peterson is, and the offense will have to evolve.

If they can either develop or add another weapon or two, and if Bridgewater, Diggs and McKinnon can continue to grow as a young core for the offense, the Vikings could continue to build on that 11-5 record from last season and establish themselves as perennial contenders in the NFC. If, however, Bridgewater continues to play at the level he has been while being offered no more weapons to work with, the one-dimensional, Peterson-heavy approach will begin to fail, and it could be a long climb back to the top of the division.