Siamese are like any other animal - each kitty is a little different. You might get a quiet, adorable couch potato.
I've had two. The first was a rescue, horribly abused. They found her shivering under a dumpster in the ghetto part of the city. Someone had done a home hack-job of declawing and spaying her, so her paws were deformed and her poor tummy was always wrinkled and scarred. She never got over her timidity, but was always very sweet-hearted and loved people. She was vocal for such a shy cat, I guess, but compared to normal "mutt" kitties, she was nothing unusual noise-wise. She was very quick to learn, but you couldn't be harsh with her ever, because she would quit eating for days. After I had her for a couple of years, she did start to purr and would approach guests and family - which she wouldn't before. So they can be taught. She never liked men though. Unfortunately, she passed away in her sleep when she was about 8 years. I miss my baby Sheebs.
Then, my friends gave me their Siamese about 4 years ago when they moved. She is the opposite of Sheebs in a lot of ways, probably because she's always been pampered. Maise is vocal and bold. She NEEDS attention. She loves to cuddle, and holds grudges forever - or until you give her a can of tuna. She is gorgeous and bonds more with people than the other pets. She will remember a person who she hasn't seen in a year and seems to develop her own little language with them over time. If she wants to sit in your lap - which she does, 24/7 - and you push her down, she will go sit across the room and sulk, glancing over at you to make sure you're noticing. If you push her off rudely, as my boyfriend will when she digs her claws into his leg, she will go hunt down an item of clothing that smells like you and pee on it! I've run through a lot of bathroom towels with her here. All the doors in my house are constantly closed so she can't find stuff. She's quite the diva and stubborn. But trainable if you're strong-willed and persistent. There's a definite pack-order with her, something I'm not used to running into with cats. She has to be reminded that she's not the boss quite frequently, and that no, she can't sleep on my kitchen counters while I"m trying to cook.
In summary, a Siamese will think he/she is your 3-year-old child. It will love attention. It will be very very intelligent. Everything else depends on the individual animal. If that sounds good to you, you certainly cannot find a more gorgeous, affectionate animal. Best of luck finding your new baby!!!