Yes, it has lots of features. Not as many as you can find on other platforms, but its not half-bad.
Yes, it's easy to use. You won't have any problems learning how to get around this tool.
So why do I say that it's 'garbage'? I wouldn't say that unless it was really, really bad - bad enough that you'll abandon it within a month of shelling out for a license.
Cornerstone is PAINFULLY slow. When I start my day, I want to do an svn update and then get working. Typically, at the command line or with other clients, svn update will take about 15s with a non-trivial codebase and a LAN connection. So how does this work out with Cornerstone?
Well, start up Cornerstone. Then wait. And wait. And wait some more. Maybe a good 5 minutes. It wants to do SOMETHING with your working copy. It isn't an svn status - that's quite fast (about 10s). No - whatever Cornerstone is doing with your working copy, it's done inefficiently and it takes a LONG time (5 minutes?)
So what? Just update while Cornerstone does its thing, right? Well, you can't. Cornerstone is stupidly synchronous and won't let you update until its finished its business with your working copy.
Want to find out what someone did yesterday? Look at the log, of course. svn log only takes a couple of seconds with most clients, right? Well with Cornerstone, you'll be waiting a good 3 minutes for it to stupidly ask your svn server for the same old log entries its requested dozens of times before. Because it doesn't cache them. Wonderful!
This tool isn't fit for use. Its clear that either the Cornerstone team don't dogfood and use their own tool, or if they do, then Cornerstone itself is trivially small and they don't realize just how bad it is with a medium-size codebase. Adding insult to injury, these guys actually have a web page where you can 'vote' for new features! Tolerable performance on a Core i7 with a flash hard drive ISN'T A FEATURE! IT'S MANDATORY!