I heard to instal just the beta you need 15 GB, is it really that big?
The download mechanism was pretty cool. It used direct links to Blizzard, and also P2P protocols from other D3 clients who have high bandwidth. Not sure if they will use that in the normal game, but it allows mass distribution of data without a huge load on Blizzard Servers. The Download was about 4GB and uncompressed is about 16GB.
So far its cool, but then again its Diablo. Game play follows the same Diablo (Fairly Linear) flow. But having 5 character classes (Male and Female) should keep this fresh. Most of the changes that have been discussed on the blogs have been rolled into the Beta. Town Portal Stone. etc.
The blacksmith in town is interesting, you can train the blacksmith, increasing his level allows him to craft better items. But I would suspect that you will never be able to craft an item as good as you will be able to get through a random drop. You have to cash in so many magic and or rare items to be able to craft an new items. There are a fair amount of items that are limited to a character class, as opposed to a specific stat.