Both dramas are action dramas with amazing action scenes and with a very similar dark and mature atmosphere.

Both were written and directed by the same people. These two drama both have protagonists that are very observant and are in the police force. SP is more focused on action instead of mystery, since you know who the bad guys are in SP right away, though there is some mystery. They also are both crime and thriller dramas.

These dramas really remind me a lot of each other. Since they're both about brothers you can expect bromance and bother conflicts from both of them. These dramas also fall under the mystery and thriller genres, though the mystery in Fallen Angel is supernatural while the mystery in Sirius is more realistic. And they have little to no romantic plot or subplot.