I personally feel it does feel like a standalone campaign rather than the first of many because of how it is. I know it's intended as a setup for more, but it could very easily be a standalone, if someone told you it was, you'd believe them. I can't really elaborate though. Spoilers. Anyway, it is of course up to you, but I think it's quite review-worthy on it's own. Especially when this project is sadly basically dead anyway at this point, so this is all there is or likely gong to be.
BTW, there's a campaign file which contains all three acts in one. Choose that one. It's one big campaign then.