I would recommend learning quantum mechanics from a textbook such as Landau & Lifshutz; Cohen-Tannoudji, Diu & LaLoë; Shankar; Sakurai & Napolitano; Weinberg; Nielsen & Chuang; Benenti, Casati & Strini; or Wiseman & Milburn; before reading Ballentine.
Ballentine makes several errors such as his discussion of the quantum Zeno effect and the outdated comments on renormalization. However, these may be incidental and minor, as even Feynman makes an elementary mistake in one appplication of Gauss's law in his justly celebrated Lectures.
What is structurally non-standard, and perhaps erroneous, is Ballentine's apparent rejection of the projection postulate mentioned in the above textbooks without replacing it with something effectively equivalent, in his discussion of filtering measurements as a means of state preparation. I do believe there are interpretations such as Bohmian mechanics, and probably many-worlds which can do without collapse or state reduction or the projection postulate (whatever one calls it). However, it is not clear to me if this is possible in Ballentine's version of the ensemble interpretation.
In particular it is unclear to me whether Ballentine's Eq 9.30 is postulated or claimed to be (partially) derived. If it is postulated, there is no problem, because it is a postulate effectively equivalent to collapse. A second mistake Ballentine seems to make is his unacknowledged use of the projection postulate in assuming that the improper mixture represented by the reduced density matrix can be treated as a proper mixture. The effective equivalence between collapse and the equivalence of proper and improper mixtures is agreed upon by Schlosshauer's 2003 review on decoherence and by Raimond and Haroche in "Exploring the Quantum".
I would also like to note that another famous book often cited for the ensemble interpretation is Peres's. There, it seems to me, instead of collapse, he postulates "blurring" of the Wigner function. I have to say I like Peres's book very much.
I do believe there is a correct presentation of the ensemble interpretation, which makes it clear that it is not at odds with the "orthodox" or "naive textbook" interpretation. This is found in Laloë's "Do we really understand quantum mechanics?"
http://arxiv.org/abs/quant-ph/0209123, where it is clear that a new postulate is necessary if collapse is rejected. For those who would like to make a detailed comparison of Ballentine's and Laloë's treatments, Laloë's Eq 37 is Ballentine's Eq 9.30, if one takes into account Laloë's footnote 41.