The well-known and now deceased F.F. Bruce, was an outstanding theologically conservative New Testament scholar, who wrote commentaries on a number of the NT books. His commentary on the two letters of Paul to the Thessalonian church is one of the best in the Word Biblical Commentary series. (It was also one of the earliest volumes, having been published in 1982). Although Bruce was a great expositor of the scriptures and wrote in a lively fashion (evident in this commentary), this is a commentary that is most useful for the serious scholar. While the layperson will gain some benefit from it, a significant portion of it is devoted to commentary on the Greek text. (Bruce's scholarly abilities shine forth in the sections devoted to this analysis.) For the beginning student of the Thessalonian epistles I would recommend either Wm. Hendriksen's contribution in the New Testament Commentary series or Leon Morris's commentary in the New International Commentary on the New Testament.
All readers can benefit from Bruce's introductory material. I would especially recommend the section in the introduction on the relation between the two letters, where Bruce does an excellent job of discussing the ongoing controversy as to which letter was written first.