If it wasn't for Bill's stubborness we would've already had this made. 
And I'm not expecting a super-realistic kind of thing. I'm sure they'll be going with a stylized look. But it'll be pretty interesting in that this will be the first time an animation team will be able to use the likeness of the actors. That's already one thing going for the film.
But GB in animation has worked before, Real Ghostbusters was fantastic. (At least, until the later seasons.) So to me, this is pretty much an extension of that, only they are using Aykroyd's script and the actual actors.
@OPMan: A remake would be way worse than this.
But yeah, while it is expensive to make an all CG movie, it wouldn't be as expensive doing it live-action: You don't have to worry about location scouting, hiring a cinematographer, super-realistic CGI (And hearing what Dan has planned, the SFX budget would be astronomical. ), etc. So it would be easier on their wallets if it took $50 million to make a CG film than a $150 million live action film.
And on the subject of GB2: I liked it. It wasn't the greatest thing ever made (Like the first film. 
) but it was a decent sequel. I just wish Columbia didn't rush Reitman and co. to make it and cut out alot of the interesting stuff from the script. (The movie was way darker than what was released.) The added Slimer bits didn't help it any either.
Which brings me back to GB3…I sincerely hope Aykroyd has a good script. The guy can write great stuff and be very creative. (The original version of the GBs was...interesting to say the least. )
It's just that I hope the jokes are funny, etc. It's already in the right direction with the setting and story...let's just hope Aykroyd wrote out the whole "Extreme Ghostbusters" angle that I heard was in one of the initial drafts. I want the original four, not some bleh teenagers.
If you spoiler me, I will eat you with tater tots.
