They're fairly well balanced — the robot ninja kills in one hit, but disappears after one kill — and
although killstreaks stack, resulting in drones being absolutely everywhere during matches, they aren't powerful enough to get annoying.
Although considered to be much better in terms of multiplayer competition, Halo 4 still ended up hammering the proverbial last nail in Halo's coffin with the inclusion of instant respawn and
killstreaks in the form of weapon drops.