Yahtzee, let me first state that I completely agree with your premise that Nintendo, normally the last developer in the world we would expect to take the easy route, did just that. We can normally expect a serious dose of innovation with each new Mario platformer, so on that front, this game is a real letdown.
However, this brings us to a question of when does this become a bad thing? One could argue that sequels are always bad because commissioning a sequel is essntially giving a developer a license to put creativity on the back burner. On the other hand, and i feel this is partly true with SMG2, sequels sometimes free up the developer to focus on the fun part of gaming, which is the gameplay, rather than having to spend the time and resources it takes to develop a completely new game from scratch. Regardless of whether you think sequels are worth the price of admission, You have to admit that SMG2 gameplay has more polish than the original... and it's obvious, at least to me, that a larger amount of effort went into gameplay rather than figuring out how to build a spherical-based platformer. The technical feats had already been figured out, so these developers got to spend 3 years polishing gameplay instead of figuring out a graphics engine. Any time a developer gets to spend more time making a game fun, that's a good thing.
Here's my rule of thumb on sequels. If a company spits out a sequel for money, or because they want to extend the life of a cool game engine, that's not cool and they should burn in hell. However, If the first game is excellent and developer makes a sequel because there were so many great ideas that they could not put into the original due to time constraints (realisitcally, even Nintendo can't spend forever developing a game), then I'm all for it. I'd prefer them to release DLC, but if it's so much content that it warrants stamping out a new disc, I have no problem with that. This is what I think SMG2 represents.
So for a reviewer like yourself, I think it's perfectly fair to ding a game for lack of creativity, even if the game is good. Regardless of how many "me too" games developers put out, creativity is still the lifeblood of the industry. At the same time, I don't think creativity has to ALWAYS involve building games from the ground up with completely new and innovative mechanics. The levels in SMG2 are spectacularly creative, even if they are based on the same game engine and exact same platforming mechanics as its predecessor. Refining and polishing an established format is fine as long as the end result is a fun and entertaining experience. For a game of this quality, I'm okay with Nintendo's decision to put innovation on the back burner in favor of superb gameplay. I see where you're coming from because it is kinda scary when a developer like Nintendo stops being innovative, but I don't think lack of innovation warrants a bad review. Innovation and gameplay are both important; innovation drives the industry, gameplay sustains it. Dark void was innovative, but the game play sucked ass. SMG2 had almost zero innovation, but was extremely fun. It would be great if a game has both, but realistically, I'll take the game with better gameplay any day over an innovative game that sucks, even if I know that the innovative game is what's driving the industry forward.
jojo