I like it, I still overpower things more than a couple of levels lower than me, simply because I have better gear, and more traits unlocked, but I can't just 1 hit every mob I walk across, but things significantly lower level than me still go down very quickly (I'm level 80, and I was running from a starter zone at the time, I was able to 2-4 hit the level 5 enemies).
I guess challenging is the right word, your hear and traits will make enough of a difference, and I rarely have to go back to low level zones anyway (usually passing through to get an area I need to my personal story).
And if you do want to play with friends, you are brought back to their level as well, and while still more powerful, you won't simply destroy everything in 1 hit, and since one of the main selling point is the whole game is meant to be fun, not just the end game, you'd be robbing them of the fun if you destroyed everything for them.
As to Inscribed's point, I can vouch for that, I was, at the time, among some of the higher level players at the time, although not part of the highest, level 80 under a week group, resulting in not many people to go on dungeon runs with, and only recently, once I had hit level 80, was I able to find a group to go through Twilight Arbor, a level 50 dungeon. It was fun, and challenging, we didn't finish it unfortunately, but some of the bosses we fought, we had to try several times till we could work out how to beat them. It was a challenge, if I was level 80 going through there against level 50 enemies, I'd be able to do anything other than boss fights solo easy, and even then, I could probably find a way to beat them solo eventually. The point is, because of the level scalling, I was able to have a fun time trying to figure out how to beat each challenge as we got there.
And it isn't really robbing you of your levels, as I said earlier, you get to keep your awesome gear, you unlocked traits and skills, and they even 'give' you levels for PvP and WvW (slightly limited in the 2nd) by auto maxing everyone at level 80 for it, and in the sPvP, even giving you awesome gear for it. While it is for balance reasons, keeping everything competitive with no one having an unfair advantage, the point is if you are looking at it as robbing you of levels, they are also giving you lots of levels at other times.
I guess the point I'm making, is it's a bold decision, that not everyone is going to like, but there a reason for it. But I like it, and I hope to see it used in other games in the future, it keeps things interesting (plus I never develop bad habits if I have been wondering through a lower level zone (say, charging head first into a enemy camp, I know I'm still going to die if I do stupid things like that, and have to work my way through)).