facetiously posted here that the Mets were in first place in their division. This was after one game , when all teams were either 1-0 (the Mets, along with the Nationals, who would go on to win the NL East, and the Phillies, who would be the last place division finishers) or 0-1. The Mets would finish the season in fourth place in the East, the worst they've done in several years. Two years ago they won the National League Pennant, but lost the World Series to the Royals. In 2016 they tied with the Giants for the wild card, but lost the one game playoff.
Going into this season, the consensus was that the Mets were serious contenders, along with the Nats. What happened? In a word, injuries. All of the vaunted starting rotation except de Grom went onto the DL at one time or another, along with important relievers. Pitching took the worst of it, but hitting, fielding, and catching were also affected.
Why? I've ventured a reply here. Is it true that injuries had a greater effect on the Mets than on other teams? According to this site they were more affected by injuries than any other MLB team during the 2017 season.
Can they do better next year? They'll have a new manager, some new players, and maybe some of their present starters, both on the mound and the field, will be gone. Others may return to top form and manage to avoid injury. There are too many unknowns to try to make a prediction.