lvls 1-30, maybe even to 40 are pretty painless..the rest..not so much. Would be a pain to solo, mobs hit pretty hard and they are tightly packed and it will take some builds, some classes longer to clear an area than others.
Just to bitch a bit more here so others can either benifit from my experience or tell me to piss off:
I am at 45 now, but we took a few days off from playing our mains because of the ridiculous repetitiveness of the mobs, I mean change the colors for god sakes or the size anything, why should I be fighting lvl 47 mobs over and over again that are clones from the defiant starting area? Shimmersand is the worst (besides the city), but many late zones look like grabage, no atmosphere to speak of, you see the same cave over and over again in which there are human mobs standing around in for some reason, but no torches, no fires, no chairs nothing..I mean common devs. Ocean floor, even near to shore looks unfinished, add some damn non hostile fish, some sea plants something...
Also, all 40+ mobs are either melee (about 50% of these slow your movement), ranged, or spell casters, but they are very limited in scope in terms of builds, or so it seems to me. I have only seen one mob type that is necro, but all the other casters are either pyros or storm. Melee are either assassin or reavers, and ranged are marks. I have yet to see a healer mob, the clerics are nearly always inquist, but often use purifer damage shields, I have seen a few cabalists as well.
Also the quests themselves, as I said, are very weak. All said, late game leveling has got me thinking about getting off the 6 month sub before that kicks in.