The only way I will have a problem with the back of the volcano being open like that is if it is truly left unfinished. Volcanoes can (and often are) blown out on one side like that, but if the interior is left open to the steel framework, that's a problem. I assume that the inside will have a finished surface (and from what I've seen it does), and if that is the case, then leaving it open is fine.
I drove by this morning and for those complaining about the slides supports being so visible, they won't be for long. As things are getting finished, the plantings are going in and really filling all that space below/around the slides. Give things a little more time and all will be fine.
As for the constant comparisons between VB and any other themed water park, you are still comparing an unfinished park with finished ones. Once the park is open, it is open season to criticize whatever you want, but until then it is still a work in progress and really can't be judged fairly. I also get the criticism of the location, but there wasn't much choice in the matter, but once again until you see it for yourself, you really can't criticize it. The plantings, water noise, music, etc. may be enough to make it really feel separate from the roads around it. Look at other parks like Disneyland, Discovery Cove, Aquatica, SeaWorld, IoA, USF, etc. All those parks are surrounded by busy roads, yet you can barely tell when you are inside them.
Also, I say the same thing to the critics that I say every time I read these criticisms. If you don't like it, don't go! Just leaves more room for the rest of us who want to enjoy it and not pick it apart.