[omegalulw]

Another key requirement that must be considered is packet ordering. With games you care about the latest state and thus discarding older out of order packets is a better strategy than waiting for packets to serialize them like TCP would do.

[Animats]

You only care about the latest state for some events. Only events which will soon be superseded by a later event should go over UDP. Move A to X, sent on every frame, fine. Create monster at Y, no.

If you find yourself implementing reliability and retransmission over UDP, you're doing it wrong. However, as I mention occasionally, turn off delayed ACKs in TCP to avoid stalls on short message traffic.

Reliable, no head of line blocking, in order delivery - pick any two. Can't have all three.