Metal Gear Solid 5 the Phantom Pain comes with two online modes.
The forward operating base or FOB sections found in the single player of MGS5TPP are a fun distraction but become increasing hard has more players level up their mother base. Trying to sneak into a heavily fortified platform with little wiggle room will frustrate some players but saying that if you manage to do it you will feel like a badass.
Metal Gear Online 3 is a good experience with plenty of fun to be had once you found a class that suits your play style. This may take a while but once you found your footing and found gear that works for you then you will start to enjoy yourself more. I really enjoyed the small class system they introduced to the game that allows for different roles on the battlefield. The biggest downside of MGO3 is that playing on your own will sometimes result in a lot of losses. While a group of friends then you will have a better experience.
For both of these modes, one of greatest aspects is its gameplay. Your characters are so responsive allowing you to freedom in you play style. You can blame team mates or lag for a bad match but rarely will you hear a complaint against the gameplay.
A rather annoying factor for MGO3 is the party system. You are able to party up with friends but at times I would often found myself put on the opposite team from my friends. I hope this will be addressed in time.
There is a dark side to these modes and that is their lifespan. As players get better gear and better mother bases, I can see the FOB mode decreasing in players. Also if MGO3 isn't supported by its community and updated by konami at times, then I can see its player count dropping. There is also the fear of konami not keeping servers running as this is what happened to the previous MGO instalments. I hope this doesn't happen, not at least until the game has a fair few years under its belt.
I personally enjoyed MGO3 over the FOB missions. It had a fun take on classes and game modes that allowed for running and gunning as well as stealth making for a multiplayer game that caters for many players.