Say what you will about the ending, but the Siege on the Citadel Beam was about a minute of the most personal and emotionally driven things I have ever experienced gaming.
Reflecting back on it, it's what Shepard had been dedicating his life to for the past few years (and us as players). All those sacrifices, all those casualties, all the relationships and people we loved and cared about, all those blood, sweat, and tears... boils down to a final all-or-nothing push to reach the beam and destroy the Reapers while staring Harbinger right in the face.
They could have retreated at the sight of Harbinger touching down, perhaps waited for air support for a quick diversion, devised a plan somehow. But no... it was now or never. Deep down, Hammer Team all knew, probably even Shepard, that it was a suicide run. They were running towards Harbinger, on FOOT.
Deep down, you almost assumed that Shepard would somehow make it unscathed. When he was skimmed by Harbinger's blast and struggled to get up, bloodied and bruised, armor ripped to shreds, it was like the most intense "Oh, damn..." moment I ever experienced. It was the first time were ever saw Shepard truly injured. Badassfully, we pictured him before as an indestructible soldier who was invincible. This moment reminds you he's just a human, and he has been just a human as fragile as any other this whole time. It's at this moment that I realized Shepard would not live.
All in all, It was the culmination of the entire trilogy, what we worked so hard for, all in that short, exhilarating minute.