No, this is NOT the best of José Carreras.
Carreras has a lyrical tenor with a soft, velvety quality - and exquisite pianissimo endings. The best example of this is, as the previous reviewer correctly mentions, the flower aria, "La fleur que tu m'avais jetées" from the Berlin 1982 recording conducted by Herbert von Karajan. Not only does this version of the aria suit José Carreras to perfection, but also the mood of the role of Don José. I have never heard another version of this aria sung so beautifully, neither by Carreras nor any other tenor.
As for the rest of this recording (I will not go through every one of the arias), there are many rather strange choices for a "best of" selection here. One example particularly is from Disc 1, I Paggliacci, "Vesti la giubba". Compared to another version I have in a collection of arias, "Classics" from Phillips 1991, this is far from Carreras at his best.
In this same collection, José Carreras "Classics", Carreras sings "Nessun dorma", Turandot, beautifully. Both "Vesti la giubba" and "Nessun dorma" are from 1980, conducted by Jesús López Cobos.
According to his biography "Singing from the soul", Don José in Carmen is one of Carreras' favourite roles. Personally I also love him as Rodolfo in La Bohème. In addition to Puccini and Bizet, I love Carreras singing Donizetti, Lucia di Lammermoor, "Tu che a Dio spiegasti l'ali" and "Una furtiva lagrima". And of course Tosca. However, even if I like Carreras with Katia Riciarelli in Tosca, I like this "dream team" as they are often called, better in "La Bohème". I think Carreras' lyrical tenor is perfect for Rodolfo and Riciarelli's light, lyrical soprano for Mimi. Also, Carreras does Lehár (Das Land des Lächelns) and Bernstein (West Side Story) beautifully. All these examples, with the exception of Tosca, are included in the "Classics" collection, and some of them also in "The Golden Years", the largest and best collection of Carreras at all. I have reviewed this recording separately.
As for Carreras' voice and his illness, I am uncertain about the effect of this on his voice the last years before his treatment. He visited Oslo, Norway, in the autumn 1986 in La Bohème, with great success. In 1987 he did the recording of Misa Criolla in Spain, only a week before being diagnosed with leukemia. Misa Criolla is one of my absolute favourite recordings with Carreras. Especially some of the softer songs here are incredibly beautiful.
I do think Carreras' voice has changed after his illness. His voice is deeper than before, but none the worse for this, rather the opposite. And the change/development may also be due to age/maturity. I heard him in an exquisite "come back" concert, much talked about here in Norway, in Oslo Concert Hall in 1990. In my opinion he has never sung better. Reviewers, opera fans, the whole opera/classical music elite in Norway were - for once - all in agreement. I have heard Carreras on other occasions, but never as that night.
However, many fans/reviewers claim that Carreras was at his best before he turned 30. As already said, I don't agree. His voice may have been stronger in his youth, but it's the lyrical quality of the voice together with his passionate singing and enormous ability to touch ones heart which I most admire and which make him my favourite tenor of all times.
Finally back to the recording in question. I think it's a combination of bad music choices plus far from the best versions of famous "Carreras arias" - the flower aria in particular - which makes this recording so mediocre.
"Carmen" with Karajan from 1982, "Misa Criolla" from 1987, "The Golden Years" from 1999, "La Bohème" (with Katia Riciarelli, conducted by Colin Davis) from 1979 and "The Romantic Carreras: Great Love Duets from 1995 are my recommended choices to hear the best of José Carreras. Plus, there are two other recordings, "The Brilliant Voice" from 1995 and "The Great Carreras" from 1994 which are superb collections, both by a younger Carreras.