I'ts coming out 8/28,..but if you pre-purchase the game then you start on 8/25,..or if you pre-order the game then you start on 8/27.
I understand you mentioned about being burned by DA2 and ME3 in the past.
ArenaNet is a different company. From my time playing the BetaEvents and Stress Test, the game does accomplish what they wanted to do in their Manifesto Video
The only things I have not tested are dungeons and of course the areas that are above the level 20.