I agree, it's tasty AJAX, plus it's tasteful design, plus it's good at being simple and not trying to do too much for you. In not trying to do much for you, it also lets you do things how you want and doesn't lasso you into doing GTD in some specific way that it prescribes. I used to use Hiveminder, but it was too rigid with its design plus the interface was too slow.

In SimpleGTD, the dependent actions aren't automatically handled; as I said before, "It doesn’t automatically add a star to items if only un-starred Actions are left in a project."

In addition, there is no built-in weekly-review procedure, but (as I said above) I actually like that because it lets me handle my work on my own without "trying to be helpful." When software tries to help me out, it more often than not just gets in my way. During my review, I look at each project separately and personally decide whether some Actions can become Next, whether new actions need to be added, etc. It's just Simple.

And, by the way, I neither develop SimpleGTD nor work for the developer. I'm just a satisfied user.