Do I think it'll be better gameplay wise? Possibly.
Do I think most people will like it more? Doubtful. Because it'll suffer the same 'sequel' effect most games do. Fans of the original will love it at first, but grow tired of the same gameplay. People who were only lukewarm about the title before won't be thrilled about it being the same thing. And those who didn't like it before will hate this one even more for being similar, especially since New Super Mario Bros Wii has come out. Classic Sequel effect.
Not to mention all 'review' sites will automatically score it down just for being a sequel. Even if it is improved in all ways.
I'm probably going to love it however. I loved the first game. One of my favorite games in the last 5 years and one of my 3 favorite Mario games. So as long as it stays close to the original or even surpasses it, I'll be quite happy.
Six upcoming games you should look into:
Essay Pro