It simply means “has it”. Inversion is often used to form questions, particularly in literary style. The T is said to be there to make it “sound good” by avoiding the hiatus. In reality, the T comes from the Latin 3rd-person singular suffix (cognate with English TH, as in “hath he”). Another way to ask would be “Est-ce que le suspense a été maîtrisé….”. It's also possible to ask the question using only intonation, but that's only possible in the spoken language, and would be informal.
“Il” refers back to “le suspense” — this apparent redundancy is typical of French. I suppose you could call it “topic-comment” structure.