I resumed playing Deus Ex again and this time went back to Detroit.

I was a bit confused at first, and then when I was given a mission to find Taggart, I never ended up coming face to face with him, so I thought I had missed and objective or something. It turns out that I had planted some evidence on a computer, thus completing an objective without noticing it.

The only real problem I found was that when I was about to leave Detroit, the game asked me if I was sure I wanted to leave, because if I did, I could no longer complete any uncompleted side quests. After checking, I found that there was a side quest, Acquaintances Forgotten, I hadn't completed, but it required me to have done some activity before I had previously left Detroit. I like to try and complete every side quest, so I as a bit annoyed that I was unable to complete that particular side quest, and there really was no way of knowing that there were such requirements.

Take it from someone living near there, you should always leave Detroit. Press A!