Will I miss out on anything by not playing Mass Effect 3's multiplayer?

Following on from Does the Mass Effect 3 multiplayer component has any effect on the Single Player component and vice-versa?

If I choose not to play the multi-player aspect of Mass Effect 3 and stick to the main single-player story, will I miss out on any single-player content? Will there be an alternate ending that I'll be denied?

Or is it more like Mass Effect 2, where you don't have to recruit and make loyal all of the companions, but it makes things easier and more satisfying in the final mission if you do?

Background, I've played 1 and 2 on the PC, and am going to be continuing with that game on the PC for 3, but don't like the PC multi-player experience and will be sticking to single-player there. I'll also be getting ME3 on the Xbox where all my online gaming friends are, so will be doing multi-player there.

BioWare has stated previously that you can gain "effective military strength" through any combination of single player or multiplayer. Single player play contributes "War Assets" while multiplayer contributes "Readiness Rating." These two things multiplied together are a big factor in your ending.

[...] SP can still be played all by itself without any kind of multiplayer or third party and you can still get the absolute best ending. [Multiplayer] just gives you new options to be able to get that ending.

Also in a different interview with Penny Arcade:

You can get best possible outcome in the game by just playing single player if you want, as long as you are willing to do a lot of the side missions and content. However, maybe you only want to do a critical path run of the single player. Well, by playing multiplayer you also increase your galactic readiness rating can affect the final outcome. Using the iPhone Datapad app and the iPad Infiltrator game will also tie into Galaxy at War and update this final rating.

However, it might be challenging to just play the single player. From this PC gamer review:

The game’s still story-driven, and it doesn’t end until you’ve completed the main series of missions. But when you do, what happens in the final cut-scene depends on how many War Assets you have accumulated.

It is possible to get the best ending in single player without playing multiplayer, but it’s twice as hard. All your War Assets only count for 50% of their potential value.

Their intent is to allow people to rush through the single player campaign (if they don't care for the story or side missions) and play a bunch of the multiplayer, and still get the "best ending."

Now that I've finished the game, there's a couple of things I'm going to add to what BioWare has said. While BioWare claims that you can get the "best ending" without playing multiplayer (or the tie-in titles for other platforms), I find this statement to be misleading at best.

It's incredibly unlikely that you will be able to get enough war assets for the "highest tier" endings to Mass Effect 3 without anything increasing your Readiness Rating. You'd have to have played ME1 and ME2 pretty thoroughly, making all the "correct" decisions in your save to import into ME3. Alternatively, you'd have to start from a "perfect" ME2 save import in order to get anywhere close to the number of War Assets you'd need. If you're not importing a previous save, your chances at playing only the single player and seeing the "best" ending are abysmal.

Additionally, you'd have to play this game through very carefully, making sure to maximize your War Assets. Most decisions in the game effect your war assets, and if you don't know ahead of time what the "best" decisions are, you're likely to end the game with significantly fewer assets than you need for some of the "best" endings.

I played fairly well through both previous games, skipped the DLC, and got nearly every war asset possible in ME3. I still fell a good 20-25% short on War Assets required for the "highest tier" ending.

Having said this, the endings are extremely similar. Regardless of how you play, you're highly likely to have very similar options in your ending choices, and each of the endings plays out extraordinarily similarly.

There are reports that it is incredibly tedious to get to full galactic readiness without playing the multiplayer:

That part is kind of cool. But the balance is incredibly harsh: I did every proper quest I could find in Mass Effect 3, made sensible decisions that didn’t conflict with my choices in the previous games, and brought people together. But I still got a gallingly bleak ending.

[...]

The only quests I had left were ones to scour certain systems for planets that aren’t marked on your map, scan them, then fire a probe and return to the Citadel. Even compared to Mass Effect 2′s resource-scanning, these are dull.

^{PC Gamer}

From that description, doing all the subquests (that could still be reasonably called real quests) doesn't seem to be enough, you need to do all kinds of resource collection in combination with certain choices made in your previous games. It's unlikely that your previous choices will be optimal, so it might be very hard or even be impossible to reach full galactic readiness.

To add to this with the BSN post by Jarrett Lee, Senior Marketing Manager - Mass Effect Franchise:

A note about multiplayer in relation to the endings

Hi everyone,

I've seen some posts where there is a bit of confusion about the ability to get the best endings by only playing single-player, because if you don't play multiplayer (or the iOS game, Infiltrator) your Galactic Readiness stays at 50%.

You do NOT have to play multiplayer to get the best single-player endings.

Here's a bit of clarification:

Your ending(s) are determined by your "Effective Military Strength" (let's call it EMS for now) bar. Focus on that bar - that is your indicator of how well you will do in the end-game.

You can maximize your EMS just by collecting War Assets in the single-player game. There is a certain threshhold of these you would need to exceed (I can't get too specific) but I can tell you there are MORE than the required amount that can be gathered in the single-player campaign.

"Galactic Readiness" is a modifier you can improve by playing multiplayer. That is to say, if you play a lot of multiplayer, you will need less War Assets from single-player to fill up your EMS bar (ie it will balance out the requirements to account for you playing in both modes). Single-player game play does not impact that bar.

EMS = success. EMS can be maximized via collecting war assets alone, even if your Galactic Readiness is 50%.

UPDATE: changing post title, "perfect" ending may create confusion. This post indicates how military strength, war assets and galactic readiness affect the endings.