I've sat in 338 and 339 a number of times in the past and it's a much better place to sit than a lot of Mets fans give it credit for. It's part of the Left Field Landing which is the second tier of seating in left-center field. There are much fewer rows than anywhere else in the ballpark, which I liked.
This section also has another name; it's part of BJ's Club House where many children will receive a visit from the mascot Mr. Met during the 1st inning. Tickets are extremely affordable too; $20 for adults and $10 for kids under the age of 12. So section 338 may not be ideal for the fans that don't have kids and don't want to sit amongst a bunch of them But if you don't mind and want an affordable seat with a solid view of the field, then sit here!