You *can* use it to make validated forms, emails and data storage with just a few clicks, but it *also* allows you to easily add gobs of your own php and js.
I originally installed it simply because I wanted to have a back-end integrated with joomla for the user -- and didn't want to try and write my own component. I got far more than I expected.
If I had to choose something to nit-pick about, it would be that the size of the edit boxes in the back-end are a bit small if you are writing a lot of code. To get around that I mirror the form code in my regular text editor where I'm happier anyway. I don't think this would be even a concern for most people though, so do not let this minor niggle stop you from installing it.
I think the fact that I had to really stretch there to find something to complain about should say something to you as a prospective user.
Finally, their forum is quite a busy place (another good sign), but Bob and Max are still very quick to respond.
Perhaps some of the more negative reviewers were playing with the *release candidates*? Those do have problems with j1.5, but that's why they are labeled rc1, rc2 etc. I imagine. They're just not ready yet.
I'm very happy with v2.2.2 as it suits our little ski club perfectly. I'd give it a 5 if it was j1.5 native, but it certainly deserves a solid 4 stars. Thanks for the nice addon Thomas.