Let me first address the second question. Primarily yes, victory points and dial advancement are primarily how the game is won. You win at the end of the round if your dial is on victory or if you have 50+ points. If tied in dial, you go in rotation order starting with Khorne. If multiple people have the points, whoever has the most wins, or else a tie is settled by the same rotation priority (Nurgle's position was very close to being relevant once). The game can also end if 5 regions get ruined, and then most points wins. Otherwise, everyone loses if the game's just exhausted, meaning the old world defended itself from the gods' war.
Now on the subject of flavor, I imagine I'd be the best one to answer this question, because the flavor still kinda turns me off. When I first saw this being played, it was with people I didn't like but still seemed like smart people. Eventually I was put into a "cultural exchange" deal where I would play this game if they played one of mine. I ended up getting quite taken with the game because of the overall design more than the flavor of how it's supposed to feel. I'm fascinated by the concepts of game design and balance. This is just about the only game I've seen that has all players working as fundamentally different, yet balanced so well that anyone can win if ignored for any significant time. It's more the styles of the characters than the "dark gods corrupting the world" feel that draws me in.
Actually, one of the thing that attracts me the most is what they're essentially eliminating with the Morrslieb set. Half the cast focuses on one type of victory and the other half is more versatile (reasonable then that they're at the low end of priority). Khorne's entire motivation is to be the balancing factor, eliminating enemy models all around the board. Everyone else advances their agenda by their own private means, but Khorne has to actively step up against them in order to win. Nurgle focuses on points more and has the best tools to make sure that works. The others have to be more subtle.
The characters' own personalities can still work out even if they don't like the general idea. Khorne is your standard combatant type; nothing too unusual there. Nurgle works with places where there are the most people to infect, but these are also the places that have the most points for domination. He's the point *****, commonly rocketing up 20+ points in a single round when he seemed too feeble to be threatening. Tzeentch is your standard control player, easy to introduce among Magic players where blue magic already fills this role. He counters opponents' moves, bunkers down in his own little home, and is often the most non-committal character that gets to be last to act. As for Slaanesh, he genuinely gets me with his flavor. I have a dirty mind, so a prince of pleasures that gets off on corrupting the heroes and nobles, that appeals to me. He also can work as a tank in general terms. It's tougher to fight him off, assuming he even lets you fight at all, and with his dial the way it is, he can still be effective at somewhat slower advancement. I've also had a game won just because I managed to use a card that gave me 1 corruption in a region someone otherwise ruined entirely on his own.
The only issue I've had with the game's flavor in introducing it to others is that it's a very male game. Granted, hobby gaming is already dominated by males, but this is especially antithetical to female players. There's just about no cooperative aspect to it; it's competition all the way. In fact, Nurgle's effects that remove others' corruption is very much like what some animals do with reproduction; remove your rival's sperm to ensure that yours is dominant. Even without Khorne in the picture, the gods are doing whatever they can to keep the other gods out of their domain. There is every motivation not to share or cooperate in any way unless one player starts to run away with the game. There is just so much dominance involved with this game; it appeals directly to masculine instincts.
Yeah, I typed a lot. I wanted to give you a solid foundation to override concerns about the flavor. I still don't really care for the flavor of the game, but the way it plays gets past all of it. It got even better for me once I got into Monday Night Combat, though I imagine players of Team Fortress 2 will also come to appreciate it the same way.