This "pre-release" version still has some bugs (for example, Endermen don't seem to work correctly in mulitplayer), but is certainly playable. You can see Endermen, towns (but not NPCs), ruins, strongholds, ravines, abandoned mineshafts, and more. The food system has been added (and food now stacks!) and there are plenty of new items to find, craft, and use. The new lighting system looks amazing (though I did have a few issues with blocks turning black). Sprining is now possible, combat has been improved, and experience can be gained, although it doesn't do anything and regaining it after death will temporarily blind you in a tornado of swirling green orbs.

Propugnator and I played for hours with minimal issues until the server inexplicably tanked, dooming us to trying to escape Creepers and Skeletons at a blistering 1 FPS. We shamelessly looted an empty village, got lost in a seemingly never-ending abandoned mineshaft for awhile, died a few times in a large ravine, and killed some poor defenseless Endermen. Oh, and someone killed me with friendly fire.

In case you need more incentive to download the "leak" or are afraid of Notch making you feel slightly bad, you can watch the official trailer for 1.8 below. Hat Films has once again created a great trailer within Minecraft which shows off many of the new features. Of course, if you don't yet own Minecraft, go buy it right now.