The Proterozoic 2.5 billion - 541 millon years ago
Not that boring really
Despite having a bad rep, the proterozoic really isn't all that boring at any point.
Highlights include: the first supercontinent; the great oxygenation event (and presumably the first Mass Extinction event); the advent of sexual reproduction; the evolution of the through gut; and snowball Earth. Also... just for laughs... the first multi cellular animals.