Let's face it: The original war was awesome, but how many got any happiness out of it? So seeing the Masters and the Servants peaceful, happy and loving each other is impossible to frown at.
Shirou and Rin's "cat-pajamas" sex-scene... or more accurately love-scene. For a refreshing change in the Nasuverse it was a moment where both parties took joy in the act, and the absolutely adorable smile that Rin wore through the whole sequence will warm your heart as much as set it racing.
The thing that Caster and Souichirou are happily married after all the things they've been put through in the original game is heartwarming in itself.
In the Hanafuda minigame Caster is shown making a lovely little scarf for Souichirou.And in their winning sequence he puts it on.