Contra is probably the most worthwhile coin-op classic available on XBLA.
In Contra, you will run around in lush green jungles, scale beautiful waterfalls, and cross icy snow deserts all while blasting the **** out of a ****load of baddies with a variety of awesome weapons. You play as one of two characters; Bill or Lance. Apparently though, you can't choose who unless you switch controllers with your buddy, as Bill is mapped to player 1 and Lance is mapped to player 2 no matter what. There is also XBL co-op play, which is great deals of fun. Out of the few games I played, a majority seemed to play fairly fluidly, and I only ran in to 1 extremely laggy game. The game controls very well, with the only exception being that shooting diagonally requires you to keep moving forward.
Like several other coin-ops on the XBLA, Contra gives you the choice of using classic or enhanced graphics and sound. Both classic and and enhanced look fairly similar, with enhanced being alot smoother. It's nice to see the effort that went into this low-budget release. You can also adjust the position, height and length of the screen (which is the tall vertical type that alot of the old arcade games on here have). The background is a rather plain orange-ish thing. Who cares though, its just a background, no one pays attention to it anyways. :-P
There are leader boards and achievements (duh). The leader boards display your highest score from your single player game at default settings. I couldn't help but wish for a little more... like leader boards for co-op mode, and maybe your high score being saved when the "The Code" is used (which is alot more tricky to enter then it should be). The achievements offer a good mix of somewhat easy (reaching the end of the first level without dying once) to fairly challenging tasks (beating the game in under 12 minutes), so no-one should be complaining about the achievements being "too easy" with this one. Also, if you think the game is too easy, you can also crank up the difficulty up to 3 more notches... but your high score will become irrelevant to ranking (and you can't get the achievements too... I think).
Overall, at $5.00 (400 MS points), this is probably the most worthwhile coin-op game on XBLA. It's just good old fashioned alien-blasting fun, either being played alone or with a friend.
UPDATE: Heh, turns out there is a leaderboard for co-op. My mistake. :-P