Will Online Games Survive the Test of Time?
Every serious gamer has a collection of old games, whether it’s dusty SNES cartridges lined up on a bookcase somewhere, or PS1 discs sealed away in a binder. While nobody remembers what connector is required to hook up an original NES to a TV, or even whether that technology exists anymore, that physical reassurance is there. Worst case scenario, emulators for old games are widely available online.
With the news that Halo 2 online is shutting down, however, we have to come to terms with the idea that online games, no matter how popular, will not survive the test of time. Even the Modern Warfare 2 and World of Warcraft’s of the world will be condemned to obscurity once that online experience can no longer be replicated.
Single player for the long run
I can have that Link to the Past experience that I had when it first came out in 1993 any time I want. I just have to load up the game and play through. While the gameplay might not have the same impact it once did, the magic of Shigeru Miyamoto will be available in its original form even 50 years in the future.
Online games, on the other hand, depend on their own popularity. Half-Life was one of the best selling games of all time, and I played Half-Life Deathmatch on a daily basis for many years in the late 1990’s / early 2000’s. I didn’t stop because it lost its appeal; I stopped playing because there simply weren’t any good servers available.

Demonstrating just how quickly online games sink into obscurity, I couldn't even find a good HLDM photo so this is from HL2 (not even the online part)
The allure of HLDM stemmed from its tight-knit community and convenience, not just its tight shooting mechanics. When everybody else moved on to Halo, HLDM was just never the same.
MMOs are a snapshot
Similarly, I played World of Warcraft obsessively for a year. While I didn’t stop because the game was declining in popularity (it’s more popular than ever), I will not be able to show anybody an experience that was hugely influential on my gaming tastes in a decade. The servers will be dead, and while it will be possible to load up the world on a private server, this would hardly demonstrate what was fun about the game.
MMOs are a living world. You couldn’t show somebody what made New York City fun if there were no people. It isn’t just the environment, it’s the interactions. WoW was great because of its community, and once that’s gone it’s gone forever.

World of Warcraft is where it's at. Halo? More like 'Halol,' am I right? SICK BURN
Nostalgia is a powerful force
While some might conclude that single player offline games are going to dominate the history of gaming because they are the only ones whose gameplay will stand the test of time, I’m not so sure. Nostalgia is a powerful force, and while it’s easy enough to load up DOOM and realize just how dated it feels, it won’t be so easy to disprove the idea that WoW was the greatest MMO of all time even when it’s just a distant memory.
As long as there are players willing to sing its praises, its fanbase will always remain. You are already seeing that in just a few short years of WoW: every time a new addition or gameplay development is released, players pine for ‘the old days’ when ‘everything was better.’ It’s hard to argue with a selective memory.

DOOM graphics have surely stood the test of time. Like voxels, or AGP graphics cards
TL;DR
In conclusion: Halo 2 was a terrible game and its servers are being rightfully shut down, and HLDM was the greatest online game of all time.
Ok, so that’s just my opinion, but there’s no doubt in my mind that online games are going to be forgotten faster than offline masterpieces. While Modern Warfare 2 is today’s flavor of the month, it will relinquish its mantle soon enough to the next king of the online shooter. Gamers have a short memory.
Games like Super Metroid, Ocarina of Time and Shadow of the Colossus, on the other hand, will be revered as gaming masterpieces as long as there are magazines, websites and fans to sing their praises.