While ArenaNet boasts that the levels hardly make a difference, (they simply add more strategy) you, and perhaps others, were painfully misled. I was.
Don't get me wrong, certainly you gain SOME power as you progress, but as my tale eventually gets to the point of, Levels do, in truth, add stupendous power.
During the beta I had my guild create new characters -- for the purpose of friendly competition (who can reach lvl 20 fastest?) and to try out new classes, and be better skilled.
Sunday night we unknowingly placed ourselves in the crucible. Aside from our weapons and armor being less than satisfactory, (we all had equipped a full set of our lvls10+ armor at the time) we quickly realized that when playing against another guild who had all lvl 20 henchmen/players (with their fine plate armor) we were at a critical disadvantage.
The opposing guild had only 2 real players (2 warriors, plus 4 henchmen) against my guild's 6 players, plus a monk and warrior Henchman. They should have had the difficulties that henchmen naturally have -- getting stuck, being stupid, not healing -- we quickly lost our Guild Hall to them, regardless of our guild skill and cooperative efforts. While we have not had our heads served to us on a platter, we were hardly a match. For the sake of credibility, we had made it to the 6th PvP map a few hours prior, but deleted our old (lvl 20) characters and transfered the items to the new ones -- so it wouldnt be whiped next month.
Point is, albeit lengthy and not-to-the-point, Different levels make a world of difference, hugely because of the armor you are able to equip, the weapons being weilded, the skills used (none of us had access to Denravi), the energy you gain, and the amount of hitpoints you aquire
