More developers need to experiment more. And I believe that gamers should be more accepting of experimentation and understanding towards developers. Ratchet & Clank: All 4 One, Full Frontal Assault; the FFXIII series, and Vanquish comes to mind for me. Insomniac Games tried to experiment with co-op gameplay and tower defense. Both games were reviewed harshly. Being a Ratchet & Clank fan, I acknowledge the fact they were trying something new, but at the same time, I felt All 4 One and Full Frontal Assault were not as fun as previous Ratchet & Clank games. They still had the charm and humor though. Insomniac Games were really humble with the reviews though. I think it was a reply to Destructoid's review, I don't remember what they said, but they never blamed the fans or people who played them.
FFXIII, already talked about. Vanquish was another TPS game, but it tried to be fast paced. Most TPS's from what I played are not that fast paced, but Vanquish was. And while it received high marks, I don't think it sold well. How good did experimenting go with that? Yet Platinum Games continues with Anarchy Reigns, a game focused on online multiplayer fighting. Low reviews, but it tried online multiplayer with a different gameplay. Santa Monica Studios is doing that too with God of War: Ascension.
I don't want to point fingers at certain games and disrespect those who enjoy them, but many games that make a lot of money have similar gameplay throughout sequels and different franchises. Games that try to be different are hit or miss. Borderlands 1 & 2 were hits with a fusion of FPS and RPG similar to Diablo and a loot system. Darksiders 1 & 2 were a hit and a miss; both combined gameplay of Zelda, Prince of Persia, God of War, RPGs, and almost Devil May Cry into one, but the success of the first did not translate to the second, especially considering THQ's status. Dishonored was a hit by being a game near the end of a generation and combining sandbox gameplay in a linear story. Spec Ops: The Line while having a generic gameplay deviated from most modern shooters by examining the dark, twisted realities of war and combat. Nier follows suit with a good story as stated by players of it, but the gameplay looked uninteresting. Both were misses.
But there are more misses and that discourages many developers to try something new. Development isn't cheap compared to last generation. And gamers avoiding sleeper hits, "unknown" titles, or games outside of their preferences hurt developers even more. How many ads have we seen with big, blockbuster, AAA title compared to obscure, new IP?
Still, there are more variables besides that. Money, economy, age, religion, area, etc.