Access requires a separate $79.99 annual subscription for each computer you use it with. Unlike trying to run a remote desktop app on an iPad, where a user has to use desktop apps in a desktop way -- sometimes clumsily, too -- Access "applifies a user's universe," allowing users to run Mac and Windows apps "as if they were made for iPad."
Naturally, there will be limitations and workarounds. The illusion is enhanced by the fact that any applications you open are automatically maximized to full screen. It only goes so far, though, as one might find it difficult to imagine Lightroom as an iPad app.
Still, the iOS gestures you'd want are all here, such as pinch-to-zoom). Access even supports native iOS actions like copy-and-paste.
Features that Parallels has included in order to cut down on frustration include SmartTap, which compensates for off-target finger taps, and a feature which allows control of sliders in apps such as Photoshop: a user simply hold their finger down for a few seconds on a slider, after which an animation will let them known that they can drag an item as they'd expect on a desktop.
You are still remotely connecting to a computer, and as such, lag due to connectivity issues will always be a potential problem. Parallels says, however, that Access has been optimized for less-than-ideal conditions.
The Verge tested it on an LTE iPad, and it was effective. We wouldn't expect a iPad connected to a CDMA network to fare as well, though.
The $79.95 subscription -- not one time -- price is a little hard to swallow, at least for the average consumer. Still, Parallels Access has a free 14-day trial, so you can determine if it meets your needs, and it the price is right.
Now the big question is if Parallels will come up with an Android version, where they could probably do even better, given Android's less restrictive nature.
A slideshow of images is available here.