I am torn on this. I think it will be busy because of the opening day but a lot of people, like yourself, may decide not to go on that day to stay away from the crowd. This means that while the Mako area may be crowded the rest of the park may not be.
Or it could just be a complete zoo everywhere.
The last big attraction like this to open probably would have been Manta, but I have no idea what it was like. I was around for the opening of Antarctica which did not have nearly the buzz that Mako does, but that day was busy in that area but not that bad in the rest of the park.