Changing and/or evolving sounds for a band tends to be a damned if you do damned if you don't. Other than AC/DC, and really Nickleback, bands don't have success making what amounts to the same album over and over. Critics hate Nickleback, but as long as they are packing arenas and selling millions of albums, that is success.
Some bands change up the sound a bit and get killed, other can change it up and be more successful. But for the most part, being stagnant in a band's sound tends to end careers.
Metallica got killed for changing things up for the Black Album and Load and reLoad, but I found those all to be very good albums. And the Black Album is one of the top selling albums ever.
Avenged Sevenfold was an unknown until they changed things up a bit and cleaned up the vocals, and big success followed.
Distrubed sounds almost like a different band now than off thier first CD The Sickness. Thier evolution has certainly helped them sell more CDs.