i think the two things that made this movie work well are: (1) the acting/performance; and (2) its brevity and flow.
the actors delivered very sincere performances and really made their characters more than just parts played...they will really break your heart. Yehuda Levi as Jagger, in particular, was very likable and made the point that he was both idealistic, boyishly-goofy, romantic; and though he may have appeared naive, his blind innocence that came across made him more endearing. (he's the boy every other boy wishes he could have for life -- and i challenge the guy who says otherwise because he's lying.) =)
as for the flow, the brevity of the film worked well because it really left the viewer wanting more. it lingered briefly (and quite appropriately) over the tender moments, but did not dwell on the sad, over-dramatic parts (that would have been overkill)...the point was made and it came across quite well under 75 minutes.
"Yossi & Jagger", though primarily categorized as a "gay film", tugs at the most visceral feelings any person (gay or straight) can have -- the comfort that only comes with genuine and true love, the intense need to be true to one's self, and the sorrow that can only be brought about by a great loss. just watch it already!