Chelsea draw analysis:

Tough opponents: Real Madrid, Barcelona, Bayern Munich
Cons: Hard to beat, need to win tactically
Pros: Mourinho has experience facing these teams (he coach RM last time).

Dangerous opponents: Dortmund, Atletico Madrid, PSG
Pros: Less tougher. More chance to win if we aren't under performed.
Cons: Less head2head record, unpredictable outcome so it's called 'dangerous'

I don't comment Man Utd because less likely will be English vs English.