I just realized from the comments that Severus is looking at James and Lily! I guess it's the die-hard Snarry OTP-er in me, but I thought it was Harry and Ginny!
Regardless of the kissing pair, I loved the grainy, wistful atmosphere. The diagonal lines create a lot of energy, particularly to the static, isolated form of Severus. They also make the pair seem more charged, more into each other, if that makes sense.
The rich colors, the beautiful luminous light coming through the windows, just make the subject matter even more poignant.