Dortmund was able to reach the finals last season, but got defeated by Madrid. Dortmund is very experienced in UCL and I believe that they will go far this season. Barcelona is in their best form and one cannot be underestimated, because they have scored a lot of goals this season. This shows that their attack is very active. However, the match is gonna be one of the best in the round of 16.
In the round of 16 of the UCL this season Dortmund will face Lille which is a team that is not so strong in their domestic league so it could be a good opportunity for Dortmund to advance to the last eight of the UCL this season. However, I don't understand why Dortmund are not so good in the Bundesliga this season when Dortmund should be able to put themselves in a better zone than now so they can return to the UCL competition next season.
I would say dortmund are very lucky. Their opponents in the round of 16 are relatively weak. Bayern munich will play Leverkusen, Liverpool will play PSG and Real mdrid will play Atletico madrid , one of the strongest teams in La Liga. On the other hand, Dortmund is going to face Lille. Lille lost 4-1 to psg yesterday.
Although Dortmund's performance in the bundesliga is irregular, this team is strong on the Champions league platform . We have seen better gameplay from Dortmund in the first round matches . So I do not think it will be difficult for Dortmund to defeat a mediocre team like Lille. The first leg match is in Dortmund's home match. My prediction is that the match will end in 2-1 or 3-1.