Integrated free into the base game for years now, Waking the Tiger was the DLC that gave China its first serious focus tree, long before No Compromise, No Surrender expanded it even further.
Nations and Content
Nationalist China and Communist China got their first playable focus trees. Germany and Japan got tweaks and expansions to their existing trees, laying part of the groundwork on which Götterdämmerung and No Compromise, No Surrender would later build.
What Changes
It doesn't introduce system mechanics as big as later expansions, but it does significantly expand narrative content and events for the Pacific theater, which had been fairly neglected until then.
Is It Still Worth It?
Being integrated free, there's no purchase decision to make. It's worth knowing about to understand the historical foundation of the Chinese and Japanese content before the more recent Pacific-focused expansions arrived.