Neil Walker is probably only with the Mets for one season, but that's a feature, not a bug. The Mets traded Jon Niese for him earlier in the offseason shortly after they lost free agent Ben Zobrist to the Chicago Cubs. The team could have come into 2016 with Dilson Herrera penciled in to the everyday job at second base, and it wouldn't have been a terrible plan, but Walker represents more of a sure thing right now for a team that has fairly high expectations.
A native of Pittsburgh, Walker grew up a Pirates fan, was drafted by the organization, and spent his entire professional career with the team until he was traded to the Mets. Following his cup-of-coffee major league debut in 2009, Walker became a major league regular in 2010 and has hit better than the league average in each of his six seasons. He's hit double-digit home runs in each of those seasons, most of them between 12 and 16 with a peak of 23 home runs in 2014. In total, Walker has a career .272/.338/.431 line with a 114 wRC+.
Over the past three seasons, Walker's 118 wRC+ has been tied with Ben Zobrist for the third-best mark among qualified second baseman, trailing only Matt Carpenter and Robinson Cano. That puts him a notch above the player he's replacing at second base for the Mets, Daniel Murphy, who had a 109 wRC+ over that span.
Depending on your preferred defensive metric, Walker has either been similar to Murphy defensively over the past three years or significantly better. UZR/150 had Murphy at -6.6 over the past three seasons and Walker at -8.9, but DRS had Murphy at -29 and Walker at +5.
The projections for the 2016 season for Walker, who is now 30 years old, aren't surprising. An established player who isn't too far into the typical aging curve yet, he's expected to hit to his career norms. It's worth noting that the switch-hitting Walker has been much better against right-handed pitchers, with a 123 wRC+ against them and an 83 wRC+ against left-handed pitchers. That could result in some starts at second base for right-handed hitters Wilmer Flores, Ruben Tejada, or Dilson Herrera when the Mets are facing left-handed starters.
If Walker just hits the way he's expected to hit, he'll be an asset for the Mets this year. While the team's starting pitching rightfully gets most of the attention, the lineup should be pretty good, too. And assuming the Mets keep Walker through the end of the season, they can give extend him a qualifying offer following it and gain a draft pick if he declines and signs elsewhere.