Cech and Sol were on frees and it hardly took a genius to spot that those two would work, although I would argue that Cech's replacement should have been a priority this past summer.
As for the rest, Kos was a good buy, Per was not, Monreal was a good buy, Mustafi is very questionable at this point, Gallas was a nutter and Sagna was also good.
Would you like me to list the failures at this point? Nah. Can't be bothered although I'd start with Almunia.