Wow just checked some previuos 1 star reviews and can't believe it!
Actually I can't remember me when I've started using this plugin :), I think it was a few month after the first release.
I understand why some people prefer AIOSEO above this plugin:
WP SEO by Yoast has many options and you need to do configure it. I guess that is something what several people don't understand or they doesn't have the knowledge.
Sure the plugin has sometimes a small bug right after an update, but these are solved within 1 or 2 days. If this is a risk and you've never heard about "testing", you should wait a few days before upgrading.
For all those comments here like
"My website lost all the google rankings after I installed this plugin..."
I know that this plugin doesn't tweak or manipulate any website (maybe some WordPress code to get it working). This will say, while using this plugin, your SEO is according the rules from the webmaster guidelines published by Google.
Maybe a website is dropped after installation, because of some nasty optimization done by the previous plugin? Or because your settings are just not complete?
I'm 100% sure this plugin will help your website's SEO or better you shouldn't use WordPress without this SEO plugin.
Thanks Joost and sorry for the late review :)