Iizuka was installed as the head of Sonic Team in 2010, and became the series' producer. Iizuka felt "Sonic" was struggling because it lacked unified direction, so Sonic Team refocused on more traditional side-scrolling elements and fast-paced gameplay. "Sonic the Hedgehog 4", a side-scrolling episodic sequel to "Sonic & Knuckles" co-developed by Sonic Team and Dimps, began with ' in 2010, followed by ' in 2012. Later in 2010, Sega released "Sonic Colors" for the Wii and DS, which expanded on the well received aspects of "Unleashed" and introduced the Wisp power-ups. For the series' 20th anniversary in 2011, Sega released "Sonic Generations" for the Xbox 360, PlayStation 3, and Windows; a separate version was developed by Dimps for the Nintendo 3DS. "Sonic Generations" featured reimagined versions of levels from previous "Sonic" games and reintroduced the "classic" Sonic design from the Genesis era. These efforts were better received, especially in comparison to "Sonic '06" and "Unleashed".