I thought I had replied to this, but I guess not, so here goes nothing...
First, some people say the Premium is always better because it's the Premium! It's got it all! I usually disagree with this way of thinking, as often the removed items create a faster, tougher game. For instance, I own a Metallica Pro because I like it about twice as much as the premium.
With that having been said, GB after much playing I decided was a Premium game for me. Amongst the reasons why...
The magna slings I love. People have issues with them being mean just like they do with the magnet on Iron Man which I love. If you play so you don't often hit the slings, they won't cause you grief. If they do, play better. To me, it's a really neat feature.
The left ramp I think is so much more interesting going under the playfield. I'm actually not one for physical locks usually, but I like this one too.
Slimer's movement, while not overly necessary, adds some interesting challenges to the game play that you wouldn't get from a static Slimer. He is big enough to impact certain shots.
Having said all this, the Pro is good too. But at least for me, those magna slings in particular make the game a lot more.
Ghostbusters has become one of my favorite games in my collection. The strategy for play is so much deeper than other games I find, and the linear modes don't bother me at all because I like how they tell a story. The only thing I don't care for is there are two video modes, the Don't Cross the Streams one is worth ludicrous points, and the other one is pure luck and pretty worthless. I tend to dislike video modes in general, and they need to be balanced a bit...