Of the Siamese I have known, they tend to be very clever and very curious, and they sometimes get into trouble when they aren't given enough stimulation--they will then seek it on their own, and probably end up getting into something you don't want them to get into.
The ones I have known generally tolerate most people, but will love one or two.
They also tend to be aggressive with other animals, either dogs or cats; not mean--they just have to assert that they are in charge. (Again, this is my experience.)
I remember Binx, a former roommate's Siamese. For the longest time he wouldn't have anything to do with me; then, after Randy got a girlfriend and started spending very little time around, the cat warmed up to me. There were several other cats in the apartment complex, but Buddy definitely was in charge; all the other cats deferred to him. The only other was another Siamese named Sidera. Binx was neutered, and Sidera was spayed, but I think they each had enough sexuality left to be interested in one another, but not enough to remember why; they fought all the time. Unless a strange cat came into their territory. Then they'd double team him.
I once saw Binx coming up the walk with a rat in his jaws. Not a mouse. A rat. Nearly as big as he was.
Several times I saw Binx chasing strange dogs--even big dogs--off the property.
When Randy and his girlfriend got married, they took another apartment in the same building; which confused Binx. He had trouble remembering where he lived; several times I'd open the door of the apartment, and in would come Binx. I'd pick him up and carry him over to Randy and Diana's place and say, "I think this belongs to you."
I say all this about Binx because he's fairly typical of the Siamese I've known. Territorial; yes. Choosy about their friends, yes. Dominant, yes. Mean? Not really; you just need to know how to deal with them. But with humans they have decided to trust, they can be very affectionate and playful. (Although they sometimes can play rough.)