Originally Posted by
Chaotix
Retinues are definitely a game-changer. I can't say whether they make the game more or less deep in terms of strategy, but they definitely change things up. I think it's also probably the way the developers mean for the game to be played.
Every culture does get it's own unique retinue type, so you don't have to play as the Byzantines to get something out of the DLC.
That said, if you don't actually want to play as the Byzantines... I honestly don't know if it's worth buying just for the retinues. Maybe get it when it's on sale, if at all?