Complex sentence: Many of these players acted as beta testers for "World of Warcraft", which was in development for release later in the year, although by spring of 2005 some returned, dissatisfied with WoW's gameplay.
Split into simpler sentences: Many of these players acted as beta testers for "World of Warcraft", which was in development for release later in the year. Although by Spring of 2005 some returned, dissatisfied with WoW's gameplay.