Wheeler was one of the most highly sought-after free agent pitchers on the market this offseason, coming in after Gerrit Cole and Stephen Strasburg in terms of quality but stood to be more affordable than either of those guys are perceived to be. As for that quality: Wheeler posted a 3.96 ERA with 195 strikeouts and 50 walks across 195.1 innings for the Mets this past season after a 12-7, 3.31 ERA season in 2018. Due to various injuries he missed the entire 2015 and 2016 seasons and part of the 2017 season, meaning that he has way less mileage on his arm than his 29 years would suggest.
Wheeler leaves the Mets for the division rival Phillies, where he'll bolster a rotation headed up by Aaron Nola but which turned in an overall disappointing performance last year. He certainly improves them.