The Banshee is a single-man Covenant aircraft in the Halo games. While they are rarely a tool (but really a threat) in the single player campaigns, they were one of the best vehicles in the original game when it came to multiplayer. Only a scorpion tank or rocket launcher could take one down with ease.
That changed espeically in Halo 2 when rockets could lock-on to Banshees. Halo 3 had even more weapons and vehicles to make the Banshee not really the best vehicle to ride.
In Halo: Reach the Banshee was great in the single-player, but it was an afterthought in the multiplayer.