Seneca, I suggest, poses problems for the admirer of stoicism. The contrast between his lifestyle and his professed philosophy has often been noted, of course. I don't think this contrast is insignificant, at least as it concerns his apparent love of luxury and avarice (the fact he held important public office is not necessarily inconsistent with the philosophy, although lust for it would be). What troubles me at the moment involves his style of writing. This may be a fault in translation--my latin is terrible--but I've read him in several different translations, and always receive the same impression.
The impression I receive is that his works are highly contrived. He seems always to be seeking to express every thought, every feeling, in as polished a manner as possible. He appears unduly conscious of an audience, one he is trying (very hard indeed) to please or impress. There is nothing heartfelt in his writing. He is often pedantic and worse yet, pompous. It's often hard to believe that even his letters are to people he thinks of as friends, rather than admirers, or those he wants to admire him. In short, there is something almost dishonest in his writing; or, perhaps, he never seems to write but for some purpose which makes it appear that it is never his true intent to honestly express ideas or feelings.
One doesn't expect such posturing in a stoic, who presumably considers the admiration of others something of indifference (although it would seem to me that a stoic could legitmately want his acts to be approved of by other stoics, for example). It would also seem that a stoic would refrain from striving so hard to appear wise and good, which I think Seneca sometimes makes a priority.
One could argue that he was very much a man of his world and time. After all, he had to survive the reigns of Caligula, Claudius and Nero (well, that of the first two, in any case, and a good portion of that of Nero) and that could not have been an easy thing. Fawning regard may have been the rule of the day for anyone trying to live who was within the notice of an Emperor. He may have been aware of the inconsistency between his life and professed ideals, and felt he had to do much to impress others of his sincerity when he could.
But there is something about him which gives one pause. He's not the man I'd suggest that someone interested in stoicism would read. For an admirer of stoicism, this is quite a condemnation.