And the friendlies are so much better it's almost like playing a different game.
I only tried this at level 13 - I'd heard the enemy AI gets super-aggressive and kills you when you're down more - they'll still go for active opponents as a clear preference over an incapacitated enemy, though, so if you're working with your team, this isn't an issue - only when you go lone-wolf.
But right from the first minute, your team will be working to achieve objectives, and if you do your part, buffing allies, distracting enemies, keeping the front lines moving forward, whatever suits your playstyle best - I guarantee you the game will be MUCH more rewarding than it can be at lower difficulty levels - even if you don't win, it feels more like you lost because you deserved it, not because the friendly AI didn't want to be worth the effort.
Friendly Medics on Normal would beeline straight at you if they chose the healing mission - ignoring enemies and dying as they charge blindly. Easy? Same deal - nobody would ever make it through even a single enemy near your incapacitated body.
On Hard, the same Medic will have you as an objective, but he'll stop and blast a few shots, either taking down the enemy, or at the very least making them take cover - then use the opening he's given himself to toss you a syringe before turning back to the fight. Seriously, they're SO much better at playing the game.
And you can ignor the primary objectives if they don't suit your chosen class - stick to Medic, and if you do well, the rest of the team will do their part too, and you've still got a good chance of success.