Imperial Latin is defined as the literary output from the reign of Tiberius through the reign of Marcus Aurelius, the last of the so-called “Five Good Emperors,” after which the character of Rome began to falter.
In earlier times, this period is often called the Silver Age of Latin, in contrast to the Golden Age. The era saw new developments and a pull away from the giants of the earlier period, which many older historians saw as a descent into degeneracy. Instead of the polished semi-Atticism of Cicero, Seneca had short, pithy sententiae and generally followed the Asianic style of the Pergamene school. Lucan’s epic is much more a polemic than Vergil’s. Elegy abruptly stopped after Ovid. The previous generation was far from silenced, though, as canonization efforts by Quintilian, Pliny, and others began to replace Old Latin authors with those of the end of the Republic and during the reign of Augustus.
That picture is simplistic, but one thing that does define the new period is a general anxiety about or deference to the emperors. Authors under Augustus were nervous, but had intellectual freedom to write borderline subversive material. Under Nero or Domitian, the same writings meant death (so Lucan and Seneca; Tacitus was smarter).
What genres were en vogue also changed. With the rule by law replaced by the emperor, the great political oratory was replaced by declamation, oratory for the sake of showing off. Satire and biting iambic poetry were verboten; satirists like Persius and Juvenal followed Horace, not Lucilius, and no one dared mock the emperor like Catullus could Caesar. The great historian Tacitus had to wait until Domitian died before he could really tell the truth, and Suetonius became popular publishing the ancient equivalent to yellow journalism. Pliny
Even in private letters, the political posturing and maneuvering found in Cicero’s letters is entirely absent in Pliny’s ten books. Instead, we have a man content with being concerned about his own literary value, whose only real politics are comprised of continually asking the emperor about what to do in any given situation.
The upside to all this was the explosion in scholarship and technical works, which may or may not have had anything to do with the growing imperial control over political offices.
This uneasiness (or, on the flip side, the servile fawning) slowly gave way to Latin of a very poor quality—with just a few exceptions—until the fall of Rome.