So the point of getting the Lieutenant packs is so you can get the figure to replace the token? Is that the only reason? If so I think I'll pass since I will already have a token to represent the Lieutenant.

They also come with a plot deck and threat/fortune tokens.

They also come with a plot deck and threat/fortune tokens.

Yes. Each of the lieutenants comes with a unique deck of "Plot cards" which are purchased and triggered using "threat," a mechanic introduced with the decks. However, there is a limit of one plot deck per campaign, and there are something like 17 lieutenants. The only reasons to buy more than a couple lieutenants are if you play a very large amount of descent, or if you're a collector or just want them for the miniatures.

So these 'plot decks' make the OL more powerful? Or just give him more options?

So far it is looking like I will hold off on buying Lieutenants and try the game without them.

AgentJ - yeah, they make the OL more powerful (with some minor mitigating benefits for the heroes.) It's definitely worth shelling out a few bucks on one, just to incorporate the mechanic in your game.

So all the Lieutenants have similar decks so Just get one and your done?

No. All of the Lieutenants have different decks with different approaches to buffing OL aspects of the game.

Is there a favorite Lieutenant that is recommended? Or one that is not recommended?

http://www.boardgamegeek.com/thread/950149/ranking-monsters-and-agents

This is a good basic review of the different agents/decks. It might help you choose one. There are also some good reviews of specific decks in the same area (strategy) of the BGG forums.

Baron Zachareth is the consensus "best choice" - he's very powerful (possibly overpowered) and fairly generic, so he can combos well with different overlord classes. I personally don't like him - I don't think he's very fun, and there are certain elements of his deck that are deliberately UNfun. I'm personally looking forward to getting/playing Verminous.