Favorite storyline mission
Easy peasy: Virmire (Mass Effect)
What begins as a lovely Mako ride on the beach in search of an infiltration team with whom the Council lost contact turns into a real kick in the quad real quick...and at least one of your teammates will die. I mean permanently die, not comic book come back to life in twenty issues die!
Battle your way through countless geth...meet up with the salarian infiltration team who informs you that Saren's base is here on Virmire. And he's building a krogan army thanks to a possible cure for the genophage. Uh oh.
Wrex gets up in your grill about that genophage cure, rightfully concerned about the future of his people. Everyone points guns at everyone. Is disaster averted, or does Wrex bite it right there on the sand?
Your team splits up- based on your decision, either Ashley or Kaidan will head off with the salarians to create a distraction. The other will stay behind and arm a nuke that you're going to use to blow up Saren's base.
Choose two more team members and lead tham into the base and find evidence of Sovereign's hinky mind-control powers with oodles of indoctrinated salarians milling about within and without prison cells. Decide their fate! Set them free, or leave them to die in the blast. Meet up with one of Saren's scientists and decide her fate- tell her to split, or kill her.
Inside the base, fight your way through more salarians, krogan, husks, and geth. Then when you come across another prothean communication beacon...effing Sovereign shows up and makes with the smack talk.
Shit goes down outside- geth are swarming around the nuke! Run back and help! But now the geth are swarming around the distraction team! You can only save Ashley or Kaidan. One of your crew must be left behind to die in the nuclear blast.
Then Saren decides to finally show up, riding around on his space scooter and throwing explosives at you.
Fisticuffs ensue! Shepard gets in a nice haymaker before it's time for the nuke to detonate. Haul your saved teammate onto the Normandy and get the eff outta there. BOOM. Have some cries.
Yes indeed, Virmire is one of the most epic storyline missions in the series. It has everything! Ah the action! Oh, the pathos! Ooh, the music!
I love the suicide mission in Mass Effect 2 almost as much, but Virmire is just the most.