If you need to sell downloadable material, Doc Seller is the only extension that offers 1)a full set of payment gateways, not just Paypal, 2) list formats with plenty of configuration parameters. No other e-commerce or downloads component has that combo.
Good stuff: Nice templatized views and professional-looking buttons (I hate amateur-looking graphics which are too prevalent among Joomla extensions), nice configurations for pricing and confirmation notices, good support for categories and all the basics. Tuan and his team are mightily accessible, including Skype (amazing) and will work their tails off to make sure your site works (and have a nice attitude as well).
Negatives: Beware of lack of support for sf404sef (major flaw but may come in a future release), improper and uneditable document dates (Tuan says this fix is imminent), and insufficient lack of config control over the columns displayed (can't get rid of the "Order It" column for one example). Overall, these are nits considering the otherwise powerful features.
With CiviCRM 3.X, it's become a stable, awesome application for Joomla. If there were a rating above "5", I would give it; it's that good.
Clearing up some myths:
The database is NOT messy - it's actually brilliant to anyone who knows databases. Clean design and essential to the incredible flexibility of CCRM. As a single example, the clear distinction and association between Contact and Member records is correct, and contrasts with the messy relationship between these with other Joomla extensions.
The conversion of the DB from MyISAM to InnoDB (required) is a small pain, but well worth the effort and straightforward. About half an hour with phpMyAdmin.
Lobo is tireless and passionate. His leadership is incredible, the guy must not sleep.
The forums are helpful and pleasant. Questions mostly get answered.
The user interface is wonderfully intuitive, so much so that it's almost training free. I needed to read up on only a couple functions to get my clients up and running in a useful fashion.
It only seems complex because the functions are numerous. But there's no fat in it. I give it an unqualified recommendation as of version 3.x.
I am stingy and usually always go with non-commercial extensions if at all possible. This is one of fewer than five Joomla extensions that delivers your money's worth.
The configurable options are many, the display is attractive out of the box and is easily modified, the iCal and GoogleMap extensions are wonderful, etc.
The only thing to watch out for is not to turn on the plug-ins for JomSocial etc. if you don't have the components installed - it will error out on you with no explanation.