At it's core, thus far GRW is very fun – with real people. Playing with an AI squad is very different and because of all the issues with friendly AI, I disliked it. After playing through all the content and hunting down medals and attachments etc, there are several enhancing tips I found for players looking for more of a challenge. I's highly recommend playing with real people and this will assume you're doing so.
Crank the game up to ghost – more of a challenge. Less chance of recovering if you fuck up.
Do not use drones. They're a cheesy mechanic that really knocks the difficulty down. The fear of the unknown makes the game much better. You'll have to monitor and track patrols, and you won't be able to just run and gun your way through knowing where everyone is.
No HUD – something we are doing next play through. Not only does it make the game look better, but it also makes you rely more on awareness, precision with shots, enemy icons do not show, and neither do team icons.
The game is what you make of it. I don't recommend going all Rambo. If you plan out an attack on a base, it's more rewarding, especially if you can do it without being detected. We also stack and breach rooms to clear them.
Few other random suggestions: try different methods of insertion, paradrop into an AO, ride up to an AO etc. Don't use tanks or heavily armed vehicles that can just wipe out bases easily.
A few other notes:
Need more enemies in compounds. Patrolling, occupying and doing things buildings. We started to find that for 3 players in a squad, there just aren't enough enemies to make it a real challenge when assaulting a base. In the snow zone, there are definitely more guys occupying bases, but still.
Theres a spot in the snow zone (forgot the name) where a gang of narco's are just standing in a circle at a gas station. You can easily just nade launcher the whole pack and they die. They def need some awareness or ai to be on lookout, hopefully this is isolated.
Expand gear options. Already theres some decent customization, but hopefully the main game releases with more than what we saw in beta.