I am in a Deadlands group ATM, it's an awesome game, lots of fun, it takes itself a LOT less seriously than most RPs, and the Marshal(GM) HAS to understand that, otherwise the game WILL suck hardcore. There's an "updated" version of Deadlands(Reloaded I think) that is more refined and easier to understand, and overall works better, but we're playing the old one. And it really is an unfinished game, there are a lot of questions a GM or a player could ask that the books simply don't answer.
There are a few features I LOVE about it, and will probably integrate into the next D&D game I run, such as open-ended damage rolls(you roll high-number on dice, you get to roll again and add it. Headshots and the like, a lot more fun than "i hit you" attacks. Basically, rolling more dice makes combat more fun. Fate (poker) chips are great for keeping players from dying but putting it on their heads instead of relying on "hand of god" GM to intervene.