I'm not a very knowledgeable draft person, but I can tell you about my Percheron mare that I got in June...
1.) She is extremely intelligent. She exploits my lack of experience whenever it suits her, so I'm very lucky that she's not an agressive/dangerous horse. However, she's also a very quick learner and knows exactly what she's doing wrong when she misbehaves, which are two things I love about her.
2.) She tries so hard to do the right thing. Usually when she gets something wrong, it's because she doesn't understand what is being asked of her.
3.) She needs a very clear leader. When I got her, she was confident and not spooky at all. However, a situation made her lose her trust in me, and for a few weeks she was spooky, difficult to handle, and disrespectful of me because she no longer saw me in charge. After a few major battle rides, she began to respect me again. That was back in August, and I think that her trust is only starting to build again now.
4.) Finding tack has been a nightmare. This might only be because I'm in Canada so most of the stuff had to be shipped from the US, but it was really inconvenient either way.