In terms of his footballing abilities and attributes Cesc does fit like a glove at Barcelona. People were talking about his almost telepathic link up play with Messi just weeks after joining the club. Guardiola even said earlier in the season that the training staff were having to do a lot of work with Sanchez to get his all round game and technique up to Barcelona standard whereas Cesc has had no problems fitting in on that front at all.
Positionally he's struggled a bit because Barcelona dont really have room for a proper number 10/attacking midfielder in their set up, which is why he's ended up playing both at centre forward and on the left at times. I think he's struggled a bit with the tactical demands of playing in central midfied for them. But he's one of the best footballers on the planet and will get it right sooner rather than later.