When MOH: Allied Assault came out on the PC, there was nothing like it before. A riveting intro not unlike Saving Private Ryan and a great single player campaign that took a long time to finish. I never play games on EASY mode. I played this on the hardest mode and got months...no, over a year of enjoyment out of Allied Assault, and it's two expansions. Just A+ production and attention to history.
Then COD came out and we had the "lean" button for starters. Things people take for granted in games now made these two franchises (at first) stand out. It's all old hat now but before it was as fresh as a Daisy.
And NEVER forget the massive amount of MODS and campaigns/total conversions these two series spawned via the fanbase communities, and which are still being created.
I haven't tried the Korean war and Word War I MODS yet.

Steam has COD 4 for 50% off this weekend which can only mean...I've got a feeling Direct2Drive are going do a deep discount on next week's Spring sale and include COD 4 and (hopefully) COD 5 in it. Heck if they put COD 6 for 50% I'd go for that too. I don't know if I should take advantage of Steam's sale or wait until the last minute to see what D2D have on offer Monday morning.
I don't think I've bought this many PC games this quickly, ever. Between GOG, D2D, eBay and Steam I don't bother with stores anymore. How about you guys?

Stores are for old people and suckers.

I don't think D2D sells COD 6.

All new controversial incidents to tackle in future COD games:
My Lai Massacre (Vietnam War)
Soviet Invasion of Afghanistan (The question is, will you play Russians or Mujahideen? Therein lies the controversy)
Japanese Invasion of Nanjing (WWII)
Playing as Wehrmacht soldiers in A campaign (This has already been requested by tons, including some developers and other industry members, but is still very controversial.)

Ultimately, announcing you're intending to release CoD 7 to 9 in the next 18 months (or so I've heard) does suggest that, yes, you're beating that horse too hard. In contrast, Blizzard intends to release the first expansion pack to Starcraft 2 about 18 months after it releases the base game (again, AFAIK).
It's interesting how two companies which are owned by the same company be so different.