Mine just arrived and I've been giving it the once over. There are a couple of features that really aren't covered / explained in detail on the sites selling the 55l so I thought I'd slam them in here.
Firstly the main compartment has the split interior that so many of us have come to love. A snow lock baffle separates the bottom third of the ruck from the top two thirds allowing a degree of control over item placement within the pack (very handy if you like to position items based upon weight). The baffle can be opened or closed allowing further control of whether to have a large main compartment or split it in twain. For those prefering lightweight hiking (such as myself), the baffle is worth its weight IMO.
The rain cover / airport transit cover is substantial to say the least - so substantial that when I opened the pack, I thought that great4camping had included another item by mistake. The rain cover fits well, with a drawcord allowing resizing. When in airport transit mode, the ruck is contained within the cover by way of a large zip (there are several heavy duty grab handles allowing for easy carrying). The cover is almost strong enough to be used as a completely separate bag, so it's pretty good. I bag everything internally as it is, so I doubt I'll use it but still, it's worth including on longer / wet trips.
There are straps on the back of the pack allowing the lid to be pulled down tight - just as one would expect, but there are also straps coming up from the base of the pack (controlling the size of the lower compartment / allowing the addition of extraneous items such as camping mat, tarp, etc).
All in all, a very tidy pack, well made and though its not what I'd call bulletproof, it's close enough that I'd be happy to handle it roughly if required. The ABS (Adjustable Back System) works well, as does the Airmesh Funnel joblette (though I haven't tested it in anger, I reckon it'll do a reasonable job of keeping your back cooler than your average pack).
55 litres is a good size for people who want the option of carrying fairly bulky loads (tarp, mat, large sleeping bag, hammock, etc) on long weekends / short week breaks. With some carfeul planning, a pack such as this could be used for longer periods but as always, it comes down to the owner rather than the activity.
At this price, if you need a pack of this type, you'd be daft not to give it some serious consideration.
Closing notes -
1. This is my 8th ruck but my first Highlander.
2. I bought some paracord from the site as well, a pretty good price and plenty of variants in colour and thickness.
Hope this helps : )