Is my initial feel wrong? It seems like people are all in it for themselves from the get-go, though as is true of most other FFG games alliances can probably be made and broken on a whim. But I know at least one of my friends hates the "surprise" dickery that the Cylons offer in BSG. Would he hate this too?
There's not much in the way of "surprises" in Runewars. (There are a couple cards that can screw a player unexpectedly, but it's not a recurring theme.) Everyone knows whose side they're on from the get go - namely their own.
The only thing that tends to catch some people by surprise is how little a role army combat can play sometimes. The goal of the game is to collect Runes. Collecting Runes requires you to take and hold territory, but not necessarily to invade enemy territory. (I mean, taking your opponent's Runes is one way to do it, but not always the most efficient.) As such, combat is something you only generally engage in if there's a significant gain to be had. Some people walk in expecting it to be like Risk or something where you attack every turn to make progress, but that's not the case.
And, how are the rules for it? It didn't seem too complicated from the promo video, but I know there is probably more to it. Is this something people can learn relatively quickly? Or is it going to be a struggle through pages and pages of exceptions?
FFG has a history for poorly organized rulebooks, but Runewars is not one of them. The basics are straightforward and easy to learn, but there's also plenty of subtle effects that you can pick up as you go. Make sure you read the rulebook yourself a couple times before the first game and then you and three friends should be good to go.
Runewars is fairly cut and dry as far as how its mechanics work. If you want something a bit more involved (and with correspondingly more complicated rules, mind you) you might also check out Twilight Imperium. A lot of the mechanics in Runewars are reminiscent of TI, but pared down and simplified for faster game play.