 Skill Points are used to unlock extra features such as concept artwork or additional outfits for Ratchet.Each game (excluding "", "", and "") also presents a "Challenge Mode", available after the player has completed the main story; in this mode, the player replays the game, facing more difficult enemies in exchange for a higher bolt payout or more powerful weapon upgrades.Games in the "Ratchet & Clank" series have been met with positive reviews, with review aggregator scores ranging from 61 to 91 on Metacritic, and 61% to 92% on GameRankings.