Dune: What makes diplomacy so powerful?

I assume you're talking about the "good" Dune -- based on the book, and the one that Fantasy Flight is kinda-sorta reprinting, not the one based on the movie.

Played it at the Gamer's Reunion. And I need to play it again because we got a key rule wrong. We didn't realize that the winning conditions change for alliances. I mean, the normal win condition is to control 3 of the 5 strongholds on Dune. But if you are allied with another player, you need to control 4 of the strongholds. If you're allied with two other players, you and your allies need to control all 5 strongholds. We thought that the win condition stayed at 3 strongholds, so when the worm showed up (which allows alliances to be formed), four of us (Atreides - me, Harkonnen, Emperor, and Bene Gesserit) formed an alliance and the other two players really didn't stand a chance. There were probably other rules we mixed up as well. I wonder if 4 player alliances are even allowed.

Anyway, what I found interesting with the alliances in Dune is a result of different player powers. More than most other games, the player powers in Dune are really, really different. Not only that, but each player can help his allies in very specific ways. For example, the Bene Gesserit can stop a player from using a certain card in battle (there are only 4 or 5 cards that are played in battle). But the Atreides player can force an opponent to reveal one of the cards he is playing (normally the cards are revealed simultaneously). In addition to that, the Atreides power allows him to see what cards people are bidding on (normally you're bidding on face-down cards so you don't know what you're getting). So, if these two are in an alliance, it's very difficult to defeat them in battle (you would need an overwhelming number of troops).

That's just one example. And allying with the Bene Gesserit is always risky, as they have the power to steal a win from you, if they made a good guess at the beginning of the game.

Another example: The Emperor player gets paid the money (spice) people use to bid on cards with. And since allies can freely share wealth, allies of the emperor essentially don't have to pay for cards they win in the auction.

Allies of Harkonnen won't have to worry as much about their leaders betraying them...

Overall, I was impressed and have to play it again with the correct rules.

I thought this article on Dune was also very interesting:
Dune

My understanding (haven't checked into this for a while) was that they were reprinting the game mechanics but not the theme effectively, so the same gameplay but without the Dune universe. Been of a disappointment personally.

Edit: Yeah, theme being shifted to the Twilight Imperium universe according to wikipedia :(

last I heard they tried for the Dune license but they couldn't acquire it.

I think I've played TI3 twice, but only finished once. Partly because I just can't do marathon games anymore (I have a family now). But I agree that it was disappointing. I didn't think the role-selection mechanic was used very well (having the one role give you -- what was it -- two VPs, when you only need 12, essentially forcing you to take that role whenever you could), and I didn't think the game was balanced very well (whoever gets to the super fighters first wins!). Also, the way it played didn't seem to match the designer's intent. It seems like the kind of game where you would have a lot of different battles going on every turn. But when we played, everyone built up for 4 or 5 hours, then there was one or two battles, and the game was essentially over.

Maybe I'm being too harsh, or maybe my expectations were too high. And yes, some of the issues could be fixed with house-rules, but that only makes the game feel even more sloppy.