No, I´m not disappointed....actually, one of the things I hate about this generation is the idea online modes (co-op or otherwise) are a necessity in order for a game to be considered "worthy".

In a nutshell, it seems this generation is seeing online modes 'eating' single player and local multiplayer modes alive, and I don´t like it :(

There's a reason why the market leader of last generation, the PS2, was not that big in terms of online gaming despite the Dreamcast having started a big trend around it. We're overestimating online, and underestimating local.

If it's half as laggy as LBP, or jumpy as Mario Kart Wii, or slowdowny as Brawl, it would suck. A game like NSMBW is better off with no online than with imperfect online. Besides, Mario is all about the local play. Nobody asks for Mario Party online.

Edit - Posting this in Gaming rather than Nintendo might garner you more support.

no matter how much you want to downtalk online co-op it always is a great _addition_ to local co-op, which ofcourse is the most fun, but can't be realized as often

Ok you say addition, should this addition become a standard of expectations though? And if it took away from the quality of the overall finished product (like very short singleplayer experiences with many games) is it best to just leave it out? 

Serious questions to ask since honestly, you should rate a game for what it is and not exactly every nit picking feature you want, if they make an amazing game with no online first go round, it should still be praised, now if they made a sequel and they really wanted to justify the new purchase, then you gotta add more modes like online co-op and make it work as well as the previous title.

Yea, having to actually be in the same room as your friends is horrible. The absolute worst. Shame on Nintendo.

There are games that should´ve had online co-op (RE: Darkside Chronicles) but this is not one
of them. NSMBWii will be all about playing with your friends locally and having a laugh.

For some, yes. For others it is a waste of time. Depending on the market you are targetting it might just be another distraction that would introduce bugs into a game. There are no absolutes in game development, or any other aspect of life really.

Online Co-op play is taxing for me, because you have to communicate verbally to work through the game, you can't point at the screen to show your idea, and if there are multiple ways to do something, there might be some waste of time debating. Competitive multiplayer on the other hand, you just need to beat the opponent, and be able to calmly swallow losing for technical reasons like internet congestion.

Does Wii-motes grow on trees or cost $5? To me this is really a single player Mario with optional co-op.

I find it quite funny that Wii fans are moaning about the lack of online co-op, PS360 fans are complaining about the lack of off-line co-op. Personally I would prefer online because that means I don't have to go near other real people...