While Milan have had a decent season thus far in Serie A, they haven't dominated opposition like they were doing last year. One thing Milan failed to do was add world-class talent in the summer, and that has hindered them this season. Taiwo, Mexes, Nocerino and El-Shaarawy are the four major signings that resonate with me, and only one of them (Nocerino) has made a big impact on the squad. With time, El-Shaarawy will blossom into a fantastic player and will be exciting to watch for years to come, but what Milan need is players challenging for positions.
When you look at Real Madrid and Barcelona, they consistently add world-class talent to a team that is already full of it. Real Madrid acquired Nuri Sahin when they have a bunch of center midfielders in their squad such as Sami Khedira, Xabi Alonso and Lassana Diarra, and it's only when Mourinho chooses to play with two deep lying midfielders that even half of those players get to play.
Barcelona added Alexis Sanchez and Cesc Fabregas this summer while they have, in attack, Messi, David Villa, Pedro and Ibrahim Affelay, yet are still willing to pay close to 40 million euros to get Sanchez. Xavi, Iniesta and Busquets comprise the best midfield in the world, and they still decided to bring in one of the best creative talents in the world in the form of Cesc Fabregas.
With so much competition amongst these sides, players are able to bring out the best in one another because they realize that in order to get onto the team sheet they must elevate their performance. Milan don't really have anyone challenging for positions except maybe left back and center back (Nesta). With the addition of the following players, Milan can finally live up to being a European powerhouse, win another Scudetto and seriously challenge the two omnipotent Spanish sides for the Champions League.