In many cases, games loose marks because they are similar to their prequels, which makes their prequels look better then the sequel, which in many cases they aren't. Basically, what I am saying is should Ratchet Future Tools of Destruction be simply reviewed as Lombax game? Of course, there is the whole storyline arc to look at, but for me, it was a totally new experience, not a similar experience as reviewers said it was. Of course part of the review should look at the differences between the two games, but for an overall score, imo, it should not suffer because it is more of the same. (sports games are excluded from this)

I definitely think the prequel should be weighed in on the final score. A sequel should improve on things and even add things. If it doesn't, why should I pay money for it and that's just something I would like to know.

No, if you did that you could essentially release the same game over and over again and get the same score without being creative.

If you really like the prequel, then it is reasonable to assume you would have like some more of that game. So I would not object to sequels that are very similar to their prequels but do add a few new little things.

I for one really really enjoyed Ratchet and Clank: Tools of Destruction and it felt quite different from the others that I have experienced actually. I suppose the shift of "only the Galaxy matters" to the shared importance of saving the Galaxy and Ratchet's guest to find out about himself was enough to make the game feel very new, fresh and different from the previous Ratchet titles.

So it seems a shift in approach to the store can also make a game feel brand new.

I wonder if Nintendo should risk shifting Mario's priorities from saving Princess Peach AGAIN to something else. How about Mario's Mansion!

Why would you apply different rules to sports games? If anything a sports game should have more leniency to be the same game as before because the sport itself goes through only small changes every season regarding rules. It plays the same year in and year out in real life, so the same should be generally said for the game.

Games like Ratchet & Clank need to advance forward because competitive games may advance the platformer genre, like Mario Galaxy and the possible new Jak & Daxter, and leave R&C in the dust. This has happened to other games. Resident Evil's gameplay was growing stale and was recieving lower scores because other games were making the gameplay look weak, where as it was fine back in 1996-1998 when it felt fresh. Metal Gear Solid's gameplay grew stale the moment people got a hold of Splinter Cell and MGS3 suffered because of it regardless of the fact that it was a superior game to MGS2. 

When Prince of Persia comes out this year, reviewers will not be hoping it plays like the old Prince of Persia games, but will have hoped it evolves past Assassin's Creed's new innovations, otherwise it will feel old.