Dota – Is possible to change the UI and icons like they were before the last patch

There are virtually no differences. It's almost an exact copy of the original Warcraft 3 map, minus the improved graphics, down to the very level of the basic controls itself (animation cancelling, etc.).

The biggest difference that you'll feel while playing it is the matchmaking system which Dota2 will take from games like Team Fortress 2 and Left 4 Dead and a ranking system about which we don't know much yet.

I'd love to give sources on this, but I'm afraid I don't have ones on hand right now. There aren't exactly a ton of interviews on the game, and most of this stuff is gathered from simply watching the game (it looks like it's an exact copy) and posts by icefrog (one of the original Dota caretakers who now works on the game) on various forums.

In some cases, the AoE/range of a skill will be displayed (centered around your hero) when hovering over the icon with your mouse. You can also view extended information about skills by hitting 'Alt' when hovered over the icon. Green text will appear at the bottom of the tooltip.