MLB midseason review: The five biggest surprises of 2015 so far

Editor's note: Most teams in MLB have passed the 81-game mark of their seasons, so The Stew is spending this week looking back at the first half of 2015.

We all love a good surprise and, in sports, we love them even more. That's why the Kansas City Royals were the feel-good underdogs of 2014. And why there are people outside of Houston hoping that the Astros can keep up their surprising success of 2015.

In the first installment of our midseason review, we looked at the biggest stories of the season. Some people were stumped that the Astros didn't get any love. We were just saving it for this post. Here are our five biggest surprises of 2015, including the Astros and beyond.

THE ASTROS
The Houston Astros haven't posted a winning record since 2008. In fact, the team lost at least 90 games in each of the last four seasons. In three of those four seasons, the club piled up more than 100 losses. For those reasons, the Astros have to be viewed as the biggest surprise of 2015.

At 49-36, Houston amazingly has the second-best record in the American League. Dallas Keuchel has led the way, and has turned himself into a dark horse Cy Young candidate. The team has also received a strong contribution from rookie Lance McCullers. Offensively, it's been a team effort. George Springer was off to a great start before a recent injury, Jose Altuve is doing his thing again and rookie Carlos Correa has looked every part of the savior thus far. It's pretty clear this team is no longer a punching bag. (Chris Cwik)

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DALLAS KEUCHEL
Dallas Keuchel had a very good second half in 2014, but nothing that pointed to him becoming one of the best starters in the majors in 2015. But that is exactly what he has become. The 27-year-old is in his fourth season in the big leagues and, so far, is putting together a surprising Cy Young-worthy campaign.

His name is all over MLB pitching leaderboards – third in WAR (4.6); sixth in ERA (2.14); first in innings pitched (130.1), complete games (3), and shutouts (2). Keuchel was a seventh-round draft pick, and didn’t exactly tear up the minor leagues on his way to the majors. But his breakout is one of the main reasons why the Astros hit the halfway mark with the most wins in the American League, and his continued dominance will be a big part of them showing they are for real in the second half. (Ian Denomme)

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THE TWINS
Rebuild? What rebuild? The Minnesota Twins are a factor right now, in the year 2015, which has not only stunned baseball fans but by now should be making fans of the Detroit Tigers and Kansas City Royals at least somewhat uncomfortable. At 44-39, they are very much in the AL Central race. To make things even more interesting, now they're adding reinforcements in prospect Miguel Sano and returning starter Ervin Santana, who is back from a PED suspension.

Whether or not the Twins are truly ready to contend is something we'll answer over the next three months. We haven't seen them post more than 70 wins in a season since 2010, so we're taking about a massive leap here if they can stay on track. If Sano and fellow rookie Byron Buxton prove to be ready that will help. But their short-term success likely lies within a veteran pitching staff that ranked 29th the past two seasons, but has advanced to the middle through June. If they stay right there, they will be an interesting team. (Mark Townsend)

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STEPHEN VOGT
Just a year ago Stephen Vogt was the third-string catcher for the Oakland Athletics who had value because he could also play first base and in the outfield. A lot can change in a year's time. Next week, Vogt will be in Cincinnati playing for the AL in the All-Star game. The roster shuffle in Oakland this past offseason made the 30-year-old Vogt an everyday player in the big leagues for the first time in his career. He has taken full advantage of his opportunity, hitting .290/.380/.502 in 80 games with 13 homers and 53 RBIs. Vogt is third in fWAR among catchers behind fellow All-Stars Buster Posey and Russell Martin. That's excellent company to keep. Vogt's breakout has been one of the pleasant surprises of the first half and a great story that shows hard work pays off.

You're not alone anymore, A's fans. We all have reason to believe in Stephen Vogt. (Israel Fehr)

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THE YANKEES
Raise your hand if you figured the New York Yankees would be in first place after their first 82 games. Outside of the Bronx, probably not too many hands. The Yankees, as they sit right now, lead the volatile AL East. That could easily be in fourth place by next week, since that division is so wild, but that's not really the point. The Yanks are 44-38, far better than the doom-and-gloom predictions they received at the start of the season.

A-Rod has been better than expected. Mark Teixeira has re-emerged as an All-Star. Masahiro Tanaka's elbow hasn't snapped. Michael Pineda has taken a step forward. There was a lot that could go wrong for the Yankees this year and so far, it hasn't. (Mike Oz)

COMING WEDNESDAY: The biggest disappointments of 2015 | PREVIOUSLY: The biggest stories

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Mike Oz is the editor of Big League Stew on Yahoo Sports. Have a tip? Email him at mikeozstew@yahoo.com or follow him on Twitter! Follow @MikeOz