Lower Level sections at Citi Field may include wheelchair-accessible seating. In section 135, the last row (row 16) is wheelchair-accessible and is often labeled 16WC. This row is located underneath the overhang on the concourse level.
The Outfield Reserved sections are located just beyond the outfield walls, and if you're sitting in left field can be a pretty good option for snagging a home run ball as a souvenir.
Sections 101-103 on the right field side are well protected by the Coca-Cola Corner seating above, which provides good shade and coverage but limits the chances of a home run landing near your seat. The left field side (Sections 132-139) has some coverage in the very back rows, but most seats are exposed leaving fans to decide whether to trade off time in the sun for a shot at a souvenir.