If you're not moving forward because you want to use your Dark set, then you have the same reason as I have my friend :-) Its not fun anymore if you finished the game before you can use the set of your choice.
I want to use other unique set as to my liking. Dark tower, dark dungeon, stages etc. I haven't used my Blizzard set as of now because of the excitement but sure I'll do.
So now I'm thinking of a new achievement. Maybe upgrading swords to thousands or completing legendary swords as I am still missing 8 of them. Today I would just enjoy what I got and be happy.
I hope that you will get your Dark set as soon as possible. Goodluck Sohan