It's fairly long if you take your time. Rushing through would make it a 45 minute DLC maybe. Definitely worth the 800 seeing as it's new content that Gearbox and such actually made themselves. Plus there's an awesome cameo to that ventrilo harassment a while back, I won't spoil it though.
I'd go ahead and get it. Achievements are pretty easy, you can find the guide for it in the main achievement guide's roadmap.
Enjoy the DLC, I sure did.
I have moved to PC gaming, so I
won't be on Xbox LIVE anymore.