From their wiki:

Although intended for general users, it is first and foremost targeted towards technically inclined users as well as former Opera users disgruntled by its transition from the Presto layout engine to a Chromium-based browser that resulted in the loss of many of its distinctive features. Despite the fact that it is also Chromium-based, Vivaldi aims to revive the features of the Presto-based Opera with its own proprietary modifications.