Some stats on the current Mets:
1) To Rurahrah's point about the starting pitching, yes it is good but not great. Fifth in NL in ERA, seventh in BAA, third in WHIP. Remember you need five starters, not just three.
2) And then we get to the bullpen. The less said there the better. 14th in NL in bullpen ERA, 14th in BAA, 13th in WHIP. This can nullify the good work of the starter. It often has.
3) Now to the hitting. We knew they wouldn't hit for average and they have not. 13th in NL in BA. But we thought the power would be there, and it has not been. 11th in HRs and 12th in Slugging %. They do draw some walks but not as many as you may think - they're 7th. The result of all this is 12th in team OPS - not nearly good enough!
4) Dare we speak of defense? According to ESPN's calculation of DWAR (the methodologies vary), there are only five players who have a positive DWAR, and three of them are catchers! I can only assume that ESPN's calculation of catcher DWAR does not take into account throwing out base stealers, where the Mets are abysmal. The other two players with positive DWAR are Lagares (who has barely played) and Frazier (an underrated defender IMO). Everyone else, you could bring up some random minor leaguer and be better off. According to ESPN anyway.
So I conclude that the Mets problems are caused by the fact that they just aren't good enough. Nothing to do with heart, guts, or any other body parts.