Finished John Dies at The End a week or so ago, now 2/3rds of the way through This Book is Full of Spiders.
John Dies at The End is absolutely crazy. It's like Stephen King meets Douglas Adams for a heavy drinking session and waaay too much caffeine.
This Book is Full of Spiders is a much more straightforward story so far. It's crazy enough to make sense that it follows JDaTE, but solid enough to stand on its own. Plus it doesn't have too much to do with JDaTE and what it does, is explained in a way that would make sense to newbies and briefly enough to stop fans of JDaTE feel like they're treading the same ground.
Both are absolutely hilarious and I fully recommend them.