I don't know what it is about but I really, really like it as a publishing system.
It seems simple, lightweight and I love the way things are broken into sections versus content and you can simply throw stuff where you will. I just ran a test migration from wordpress and while I know I am going to have to deal with ironing out the cruft I've built up over years of not having a good structure there, as well as new stuff from changed migration while that script has not been updated, I'm kinda leaning towards mephisto, on the new hoster. I also find it much, much easier to modify and its design much simpler than the venerable (and yet excellent all the same) wordpress.
The guys who are working on lighthouse are slowly updating it. The latest dev version is at 0.8 and I am waiting for someone (I wish it could be me) to fix rpc-xml posting so I can use "MarsEdit":http://www.red-sweater.com/marsedit/ with it (which I'm writing this with right now), but other than that, not a lot of complaints right now. Plan to add in tag clouds and flickr photos and leave it as lean as possible. Will try and up the changes I make to the wordpress migration script.
For some reason it fits in rather well with the way I work generally as I can
svn co plugins down and update it like a dev and deploy via capistrano once I've got things going.
I also particularly like the way they've used liquid a la shopify as a templating language. Really easy to change things. Much easier to figure out how to mod a theme than say typo or wordpress.