Can u just go to this show or do you need to plan ahead for seating?

No reservations or tickets necessary. Just get there about 45 mins beforehand.
There is a dining package available that guarantees a seat, though. In most slower part of the year, it is not really all that necessary. (No additional charge if you are on the DDP.)

We have done it with and without the dining, and got good seats either way. It is a huge theater so unless you try to get there at the last minute in the middle of peak season, you will have good results.

If you do a search on a term like "Fantasmic Dining Package" you might find threads with more details and feedback.

Hope that helps.

We've done both ways too, and I highly recommend the dining package. It doesn't cost any thing other than eating at a specific restaurant. I HATE crowds, but can manage WDW for most everything. The big exception is how freaked I got standing in wall-to-wall people for an HOUR waiting to be let in for Fantasmic! It was in the "off-season" which isn't all that "off" anymore. There was only one show per night.

So this past trip, I used one of my TS credits for Fantasmic pkg and Mama Melrose. They "held" the ressie with my CC and there would be a fee assessed if we were a no-show or canceled within 24 hours or something like that. If it rains and the show is canceled, you're outta luck. However, it doesn't COST anything extra, so no biggie. I LOVED being able to stroll into the theater 15-30 minutes before and get a great seat. Here's a picture of the crowd 30 minutes before the start of the show in "low season" October:

Fantasmic crowd pic (http://farm3.static.flickr.com/2181/1736345711_3ff2a9bf08.jpg)

Sorry it's blurry, but you get the idea.

It doesn't cost any thing other than eating at a specific restaurant.
This is true if you are on the DDP. It only costs you the one TS credit per person just as if you were eating there anyway. However, unless something has changed, if you are not on the dining plan, I believe it is a set price, which varies depending on which eatery you go to. However, with that set price, you did get pretty much the same choices as the DDP. For example, with Mama Melrose, for the set price, we got a special menu that gave us a our choices of appetizers, main course and desserts - all included with the package. (I am not sure if that menu was different than the usual menu as we have not eaten there since.)

Of course, if things have changed, I will yield to the more up to date info. :)

In essence, if you are planning on eating at MGM and you want to go to F! anyway, then the package surely does not hurt.

Yes, the stands can get kinda full, but it looks worse than it is. (In other words, I never felt jam packed crowded.) The bigger problem is getting out of the park afterwards. It takes a little bit of time, but just reflecting on the show makes me forget about the wait. :) I was shocked during our last trip when people started to leave about 5 mins before the end just to beat the crowds. (It was kinda rude, to be honest.)

The bigger problem is getting out of the park afterwards...I was shocked during our last trip when people started to leave about 5 mins before the end just to beat the crowds. (It was kinda rude, to be honest.)

It's always amazed me that people will leave an event before it's over. I can almost understand a big game where the score is lopsided. But how many games have been played where there's a big comeback in the final seconds? And with a show like F!, it just boggles me that it would be more important for people to gain a few minutes on their way out than to watch the full show! I solve the end of show crunch by just staying where I am and watching all the masses cramming into the exit. I simply wait 10 minutes or so till the crunch is over, and then saunter out to my car - simple!