It's one of, if not the best looking games on the iPad 1 and iPhones prior to the iPhone 4S. It's a very fast paced shooter and I think it is the most entertaining shooter for the iOS, despite the character walking for you.
In my opinion, it being a railshooter is not as much of an annoyance as when you get hit by the enemy - then (if you are playing it on an iPhone) the phone shakes/vibrates, and that really annoys me and there doesn't seem to be a way to disable it.
The iPad doesn't vibrate though, so it shouldn't be an issue for you.
It can take a little to get used to controls wise, but it's an entertaining game nonetheless. There are not many levels (3) besides a few rehashes of the same and harder difficulty settings. There's also a museum mode where you basically walk through the level like in a museum and look at the visuals, as they are very good considering the device specifications.
I have it myself on my iPhone 4 and I have made a little screenshot gallery that you can check out:
http://www.dropbox.com/gallery/26144715/1/Rage%20HD%20iOS%20Screenshots?h=53263b
Dropbox apparantly decided to JPG-ify all the images. Click the 'full size' button for each image to view them in their true quality
