Yes the robe opens in the front. The main difference as far as visible styling tweaks they made for each film is the way the "streamers" hanging from the arms are cut and the way they bottom of the robe is cut too. These are just a few of many differences.
Also I noticed a few people way back posting about how the costumes opening in the middle attached. There were never ANY costumes used for either film that used a zipper.
Heres a few insider details I picked up over the years about the costumes in general, then after I post more pics of mine later today we can get into specifics about mine.
For each movie about 3-4 costumes were made for the killer. In Scream 2, the costumes that the movie goers in the audience (the extras) were given were NOT the same at all. A lot of people think they are the same material and design, minus the attached glvoes but thats just not the case. They were a different design and different fabric as well. As I said above, the actual killers costume fabric is expensive. Around $300 for each robe. The only theater going extras in Scream 2 who donned an actual robe were the two using the urinals when Phil Stevens walks in the restoom. Aside from cost, they made the robes different mainly because they wanted the actual killers appearence to be obvious. Having his design different from the others made it scarier.
Another interesting fact is that there were NO sizes for the killers robe. They were all made to the same dimensions. If you notice, unlike other movie maniacs and slashers such as Jason and Michael Myers, Ghostface gets no credit in the credits. Thats because for each movie, they used several stuntmen and body language actors to play the part. They may have one guy play him for one scene of him running, and then another guy in scene that requires a hard slam/fall or other stunt. Also keep in mind, the actual actors playing the killers in the film would often don the costume at some point. Especially the ending of Scream 3. Scott Foley keeps the robe on the entire time (my robe).
Anyways, its because of this that in order to ensure fewer costume fitting problems all the costumes were made the same size. A little large. Thats one of the main problems with the replica that I saw photos of on michael-myers.net. The gloves are WAYYY too small and tight. The gloves on mine, and all the screen used ones are very large and baggy. Just compare the pic I posted of my glove to the replicas gloves. Even watch the films and pay attention to the gloves. They are baggy there as well.
For reference purposed I can tell you Im 5'11 and weigh about 145 pounds. The costume fits me fine. It fits exactly the way it does the actors or stuntmen in the movie itself.