We have a 30+ years old Sennie, Rikkie. We adopted him last May, so I feel I can add my two cents here now.
The Good (in random order):
-He is very friendly, whenever we have visitors, or go to visit, he often asks people to scritch him, he is usually calm and quiet.
-He is very affectionate (mostly towards me, though. My wife is able to scritch him most of the time, but when I'm around, he hardly has eyes for her).
-He seems to have a sense of humour; He has the ability to burst out laughing when we make a joke, or laugh ourselves. His timing is impeccable
-He is very forgiving. He is my first parrot and the mistakes I make do not seem to bother him for long. When he does bite (not that often), it is not too bad.
-He has had to learn to play by himself, but it goes to show that they are never too old to learn. He can now destroy his toys for hours on end.
-He really enjoys the attention he is given. If he wants more, he can make the cutest little noises and actually talks (Come, come here, come on then (in Dutch))
The Bad:
-He thrives on attention and company. He does not like being left alone when we leave the room., even for a minute. His screams are really loud an really get on your nerves. Some days are worse than others.
-He is jealous; When my he is with me, he can be unfriendly to my wife, although he rarely really bites her. This might also be due to the fact she is really good at reading him. He really dislikes our dog (a miniature poodle, although I do not think her size is a factor for Rikkie). When he gets the chance, he will walk to her bed and try to harass her. Of course, we do not let it get to that point.
-He can often get cranky around bed time. If he notices I'm preparing his cage for the night (cleaning it up, changing his water), he will often refuse to step up (although bribery with a treat is always an option; usually successful). When I drape the cloth around it, or remove his bowl of fruits and veggies) he can sometimes try to attack my hands through the bars).
-He needs to be in his cage when we eat, or he will climb up my legs to join in on the fun.
The ugly:
-Pooping everywhere, but this is of course not species specific. I can often feel him squeezing his feet just before, but I'm not always in time
-I know it's natural for parrots to choose one partner in a household and I am the lucky one. Although my wife and i know this, I sometimes feel bad for her, because he is not as close to her as he is to me.
-He needs attention. Of course he should get it and he deserves it, but some days are worse than others.
Again, most of these traits are common for all parrots, I know. My wife and I had talked for years about having a parrot, we took care of a couple for a few months, so we had a good idea of what it would be like. I would not miss him for the world now and I am forever grateful to my wife for finding him and taking me to go and have a look at him at the halfway home he was at...