Great matchups.
Barcelona vs Atlético : Won't be as easy as people might think. Atlético play very well against Barcelona because their playing style is a great match for Barça. Atlético play off the ball, most of the time the opponent dictates the position but Atlético play great team defense and use counter attacks to score goals. If they manage to lock Barça up, they might get lucky.
Real vs Dortmund : These teams are nowhere close to what they were when they faced up in last year's semifinals. Real look very dominant and Dortmund have lost some key pieces. Should be fun to watch but I expect Real to go through with ease.
PSG vs Chelsea : Now this one has the potential to be the best matchup. Chelsea play very well on their home, they play some intense defense and dictate the tempo. On the other hand, Paris Saint-Germain has a much better attacking line with Ibrahimovic, Cavani and Lavezzi. I think this one all comes down to the game in France, should Paris get a clear result, they'll run out as winners.
United vs Bayern : Easy one. United's weak midfield will look ridiculous against Bayern's passing and tenacity.