The Huey UN Pilot campaign (comes with the module) is pretty nice but a good few missions are buggy as hell as there's some confusion in the waypoints altitudes (sea level vs above ground level) making your leader go onto wild altitude changes that are tough to follow. Going through it makes you a better pilot at any rate, and otherwise you have the option of taking the campaign mission files into the mission editor and fix the waypoints.
There's a nice free player-made campaign called Bay of Hogs. It was originally made for the Mi-8 but the author has ported it to the Huey so you can pick your favourite. It's pretty entertaining, being based on over-the-top movie-grade manoeuvering. No fooling around with systems or weapons, it's all about the flying. Say you've got to take down a truck on the road, your gunners behind will open the doors and fire automatically once you're in range. Speeding a few meters above ground, flying under power lines, bridges, small rooftop landings in the jungle, night raids, you name it. Not sure how well it plays with the new version of the Caucasus map though so maybe it needs an update.
Haven't started them yet so don't take that as recommendations, but I've also got Argo and Oil Field in my to-do list. Argo is a ship-based Huey campaign with varied objectives and great reviews, and Oil Field is a civilian campaign for the Mi-8 which sounds neat for a change.
