I though the Halo 1's single player of very good.  Especially certain levels with the flood in them.

Halo 3 will likely have a good enough single player campaign to satisfy most people (Bungie got a huge amount of flack from people who were disappointed with Halo 2's single player campaign being cut short and have stated they're working hard to make sure people aren't disappointed this time around).

I agree though about multiplayer, it definately is where Halo shines.  There's a reason why millions of people spent many hours online playing it and why there are still many thousands of people playing it at this very moment.  Any game that has people devoting thousands of hours to it and eager for the sequel has to have something going for it.  That's why I find it hard to take people seriously when they try to put down the series, I mean if the series was no fun it wouldn't be anticipated at all, and isn't the most important thing about a game is that you're having fun?

You've played MGS 4? Is there online play for MGS 4? I didn't know any of this...

I believe Hideo Kojima has said that there would be online in MGS4 and they're improving on MGS3's online for it, but that was a VERY long time ago when I saw that.

As for the OP, I don't think the Halo series would be as popular, but would you consider hooking Xbox's up on a LAN in the same building as online? While I did get bored of Halo after the first time through, the multi-player was very fun and it wasn't an online game and systems had to be hooked together (usually in the same room for night parties) to have 16 people playing. However, I think Halo 2's popularity would have taken a hit if it wasn't for it's online play, but I think off-line LAN's still would have thrived.

It'd be good/passable, but you wouldn't get the full rich reason that Halo is so popular.

Thats like asking if Goldeneye is the best N64 FPS without the 4p split screen.

 Yes i do agree, and while i stick by my opinion on halos single player i must admit that my perseption on things must not be taken to seriously. I have only had an Xbox for a few months after i picked one up for less than the price of a game and have been playing halo and halo 2 extensivly, both in single and multi-player, and yes, the single player has a decent story, slick controls and good A.I, but it still felt like any other FPS. But perhaps its the fact that i didn't really play it when it came out. I understand it did a lot for the genre back then and i am not really getting the full magnitude of its impact. 

It could very well be that all the other FPS' are like halo rather than the other way round. But still hear me out on this s2puzzy; as long as you have more than one controller you'll be fine.