Choosing good addons for the flight simulator can be a challenge. So here are some good addons that I use for my flight sim.
Number 1 on my list is AirlineAnnouncementsV1 which adds custom airline announcements to the flight sim.
Number 2 on my list is the GNS430/530 enhancement pack from Working Title. This replaces the default ones that come with the flight sim. It is a great enhancement which has many features. This can be downloaded from the in game marketplace.
Number 3 on my list of addons for this sim is my own addon. This enhances the default ground textures. Get it here: https://flightsim.to/file/40348/hayes-simulation-improved-taxi-marks-and-ground-textures
Number 4 on the list of addons is the 40th Anniversary Enhancement for the sim. This is by GotFriends and it improves a lot of things for the planes recently implemented.
Chapter #1: Expansion Features (Released)
DHC-2 Beaver: Added 35" Bush Wheel Variant (Includes All Liveries)
DHC-2 Beaver: Added Water Spray Effect to Amphibious Variant
DHC-2 Beaver: Added Hide/Unhide Option to Tablet
DHC-2 Beaver: Added Start-Up Combustion Smoke Effect to All Variants
Chapter #2: Expansion Features (Released)
Global: Added "40th Anniversary" Effects Dependecies as Stand-Alone Effects
DHC-2 Beaver: Added Ski Winter Kit to Standard Wheel Variant (Option on Tablet)
DHC-2 Beaver: Added New Custom Snow Physics when Skis are Attached
DHC-2 Beaver: Added New Bush Tail Wheel to 35" Bush Variant
DHC-2 Beaver: Added Low Fly-By Dirt Effect
Douglas DC-3: Added New Amphibious Float Variant (Includes 2 Liveries)
Douglas DC-3: Added Custom Flight Model, Weight Limits, Drag Limits, and Additional Float / Fuel Tanks
Douglas DC-3: Added Water Spray Effect to Amphibious Variant
Douglas DC-3: Added Start-Up Combustion Smoke Effect to All Variants
Douglas DC-3: Added Wheel Landing Effects to All Surface Types on All Variants
Douglas DC-3: Added Water Rudder Switch (Replaces External Power Switch on Amphibious Variant)
Chapter #3: Expansion Features (In Development)
Douglas DC-3: Planned JATO (Jet Assisted Take-Off) Variant
More Additional Features: Taking Recommendations in Comment Section
Credits:
Jonx: 3D Model Merging, XML Modifications, Flight Model Modifications, and Sound Modifications
Mykrode: 3D Modeling, Texturing, and Animations
Twoseventyinc: Texturing
The Final Addon that I am going to shortly talk about is the Reims R172 for MSFS. It isn't fully realistic but it has some cool features. You can check it out here: https://flightsim.to/file/42097/rf172-reims-rocket-cessna-r172-hawk-xp-ii 
I also have made a YouTube video showing some more mods and my opinions more in depth. Check the video out here: It will be coming out at 11/23/22 at 5:00 PM CST