Just played it again with my kids tonight. We still have several microgames to unlock (and when you get them all there is a new minigame unlocked). We've put at least 10-15 hours into it so far. Also, we've only made one attempt at unlocking all the elephant levels (have 2 of 4 only so far).
I think the people saying 3 hours are being a bit ridiculous. Yeah, that might be how long it takes to power through to the credits (if you are really good). But there is SOME unlockable content in the game. Maybe not as much as the GBA versions, but some nonetheless. We are still a few hours from getting all those microgames (I just figured out tonight you could see which ones are still locked within each story - d'oh!, I had just been guessing before). By the way, that's where the flowers are in this game (you get one for each "story" as you unlock all the microgames for it).
And all of this is just on my son's game. I still have my own game to play through and unlock everything, and my daughter wants to do the same.
And I'm not even talking multiplayer here.
So, while I can see $50 being a bit much for it, I think it is definitely worth $30, and you will probably be able to get it for close to that with some deal or another in the near future. If you have more than one person in your household interested in playing (single-player or multi-player) it makes it much more worthwhile.