I don't think he's downplaying Halo in any way. He's just wondering why this event is even occurring? Why say "one last time"? Is MS gonna kill HaLo 3's servers also? 

You say it like it's true.

Fans have fond memories of the game. They haven't played it lately though do to other games, friends stopped playing, etc. They decide to rekindle the community and start playing again. One last time maybe implys that they will move on to present games after that.

Though I would argue Halo 3's community is still active enough for this not to be needed. I mean it still almost always appears in the top 20 activity charts.

Edit: But then again, the best aspect of Halo 3 imo was custom games, and this certainly would make sense if the people participating would host all kinds of fan favorites.

It is true.

Doom was the best until Quake. Quake was the best until Half-Life and Half-Life was the best until Halo. Nothing since Halo has bested it. There have been some great FPS games in recent years, but I always come back to the Halo series and it never gets old. I've replayed each game several times. I've mad a tradition out of replaying the entire series right before a new Halo releases. It never gets old, just like Mario, Zelda and Metroid. It's so fundementaly fun to play that it's like Halo goes beyond just being an FPS and is it's own sub-genre. That's why no other FPS feels anything like it.

Halo is THE standard for which all FPS games are judged.

I thought call of duty was, considering every fps these days is compared to it

Halo was last gen though, although i prefered timesplitters.

Call of Duty is high quality, no doubt, but Halo is better.