Reach isn't technically the end of a franchise, though to me it's the end of the "true" halo series. 343 may be picking up the Halo brand from here on, but it'll never feel the same to me without that Bungie logo. Not that that's necessarily a bad thing.
Anyways...
That ending really stuck me in the gut. You start the mission, and your new objective flashes on the screen: survive. Take twenty steps forward, and you see the broken corpses of fellow SPARTANs littering the corners of what remains of a ruined building. The covenant's waves grow stronger and stronger as your ammo dwindles and your visor cracks, until Noble 6 finally takes one bullet too many, but defiant to the end as he is, goes down engaging multiple elites in hand to hand combat.
The worst part is that Noble 6 will never be remembered. As a black ops agent, despite the fact that he was mostly responsible for the survival of the human race as we know it, the only person who will ever know this is Dr. Halsey.
Also, Portal 2 for obvious reasons, though I would be very surprised if Valve didn't shove a sequel to that out the door at some point. Though, it's been shown that Valve can't count to three.
Oblivion, though many will probably disagree with me on this, had a good ending to the main questline, in my opinion. It was a cruel reminder of how insignificant the PC is in the grand scheme of things and how cruel fate is, yet was also suitably epic and made me feel like a hero. I think it set the scene for Skyrim perfectly, because playing as Dovakhiin will have all the more rush to it when your realize that every previous PC in the series, despite being one man armies in their own right, were just setting the scene for your fight. It's a bit like going back to the original Halo trilogy after beating Reach, having that knowledge of who fought and died to put the PC where he (or she) is now.