Complex sentence: Work immediately began on a pseudo-sequel titled "Dark Chronicle" ("Dark Cloud 2" in North America), that, while not as successful as the first, still gained critical acclaim and sold over half a million units worldwide.
Split into simpler sentences: Work immediately began on a sequel titled "Dark Chronicle" ("Dark Cloud 2 " in North America). While not as successful as the first game,"Dark Chronicle" still gained critical acclaim and sold over half a million units worldwide.