A couple things.
whitespace is intentional; see Edward Tufte for example. If you don’t like whitespace, you are free to change the CSS to your needs. We like whitespace with the default design.
mouse over the symbols to see what they mean, provided you are on a mouse capable system.
mouse over the times to see what they mean, provided you are on a mouse capable system.
the post controls are dimmed until you mouse over them to reduce noise. This is only possible on a mouse based system, on a touch device they are full opacity all the time.
Please do spend some time browsing around before offering feedback, particularly on aesthetics. That said – the default design is not the final word on how every Discourse forum will look, any more than the default template that ships with WordPress is the final word on how every WordPress blog will look. If you want to build a custom CSS theme to taste, this is totally supported!