It's still been very successful for an indie and will probably be at the top, in the top 5/10, for the rest of the summer. I don't think this is any cause for alarm. This game has been a smashing success and the champagne should be popping for weeks to come over at Larian Studios.
Dishonored was a fun game of a different style. I probably liked it more because it challenged me not to be rambo and just whack everything in sight. For an action game it had some style and depth.