I play retro 2D Mario games with my best friend in the same room when we decide to do co-op and it's so much fun. I doubt we'd be able to replicate that much fun together online, with online lag and Wii Speak and such. I really don't care that it doesn't have online personally. A missed opertunity? Probably, but there's always next time huh.
My biggest gripe with this game is that it doesn't have its own original god damn theme, i didn't really like New Super Mario Bros. for the DS' soundtrack or main theme, i didn't feel it was as strong as previous Mario titles music and i'm quite upset that they recycled the main theme for use again in this game. Also, the Toad's... there was no explanation for that, they could have at least had Toadette for crying out loud instead of Bucken-Berry and Ala-Gold.