You can download drupal-8.0-alpha3 or clone Drupal 8 in git:
git clone --branch 8.x http://git.drupal.org/project/drupal.git
Drupal 8 is full of significant improvements over previous versions of Drupal, but many Drupal developers and contributors are understandably concerned about the scope of changes from Drupal 7, and how much they'll need to re-learn. The folks at flink have taken a lighthearted approach to this problem: "Ride the tiger, don't fight the tiger."
Read more: Drupal 8: to embrace or to brace yourself?
The article's tone is perhaps a bit irreverent, but it is refreshing to read. I personally haven't found learning Drupal 8 development any harder to learn than learning Drupal the first time -- though, honestly, it was never particularly easy. The advantage that Drupal has is that there's a very strong community of developers and trainers creating material to teach and explain even the oddest bits. One of this site's goals is to aggregate and promote such material for Drupal 8.