User blog comment:JAlbor/Dishonored Interview Opportunity/@comment-72.80.222.252-20120930160831/@comment-99.159.4.25-20120930202006

the game is not full open world so there isn't anything after completeing the game (the game does have a ton of replayability such as multiple endings, the numerous possible ways to handle the missions, the fact that you can't get all powers in a single playthough, randomized clue and target locations, harder difficulties, altered dialogue based on your chaos rating, and other various aspects designed to give the game a ton of replayability.

no you can't pick up weapons. You have Corvo's sword, the crossbow, and the pistol, along with your various powers.