The answering persons here are users of SL the same way you are.
I agree, this time the update is *bs* as it has not some minor glitches, it just plain simple doesn't work at all and there is simply no chance to make it run somehow.
I tried everything: reinstall, redownload and reinstall, clean reinstall, release candidate viewer install. Nothing changes, you won't get to log in or even start the viewer. It just quits.
If you want to log into SL, you simply can't do it with any LL viewer at the moment.
So there's two solutions: take a break and try to update the viewer in a couple of months and see whether it works by then, or get a thrid party viewer that works.