I can only speak for my horse, but compared to other horses I own or have been around he is very intelligent. There are pluses and minuses to that. Keeping his mind busy is very important. But he is completely honest and will try with all his heart to accomplish what you ask. But it took building a partnership and coming to a mutual understanding to get that level of commitment. He already knows way more than me, so when I try something new and finally get it, it's comical to literally hear him take a big breath and sigh as if to say thank goodness the idiot finally figured it out.
If he hears me at the barn he's instantly nickering and at the front of his stall.
He's not quiet like some QHs. But he's not hot or out of control. It's hard to describe... he will focus on whatever task, but nothing escapes his attention. He's not ADD or not listening/looking all around, or have a short fuse, rather just constantly aware. I wouldn't call him reactive or spooky. I've been on more QHs that have pulled mind boggling teleportation moves than him. If something really bugs him, he will think about it, huff, then react. It's so methodical and gives me plenty of warning to redirect him before a reaction. Personally I think it's just his way of asking the boss if all is ok. As long as I communicate back, he doesn't take matters into his own hands and think for us both.
Morpheous has loads of energy and endurance. Unless it is ridiculously hot out, I'll usually reach my physical limit before he ever breaks a sweat. To manage that energy he gets ridden 3 or more times a week. Anything from dressage, hunter, jumper or trail.
It's a lot like nuts and bolts - if the rider's nuts, the horse bolts! ~Nicholas Evans