My twin boys are 20 months. . . getting closer to two everyday. Things are definitely easier than they were a couple months ago--18 months was really peak misery in our house. Since then their language skills have really developed a lot to the extent that they can mostly tell us what's bugging them or what they want/need. I think their frustration levels are lower than they have been, though they can still get pretty frustrated. Of course, all the difficult behavior is pretty strongly linked to hunger/exhaustion. It is just so hard to keep them both well rested and well fed all the time!
I still have moments of saddness every couple days about the fact that I have twins and all that that means. I hate that I have to bring the twin stroller with me everywhere I go, instead of just popping my tot onto my back (my guys are so jealous of each other being carried that I can't do the one-in-the-stroller, one-on-me thing anymore). I hate that nursing in public is such a huge ordeal (they absolutely have to nurse at the same time). I hate that I get so bogged down with the cleaning and washing and feeding and nose-wiping that I sometimes feel like I don't get to enjoy my children as individuals.
My sister is expecting her first baby, she has the same due date (3/3) that I had but two years later, and I find that I am feeling so jealous of the fact that she's just having ONE baby. It will be such a different experience for her. I thought I would be past all my negative feelings re: having twins by now, but I'm obviously not. It is nice that my boys play together, but in many ways I am seeing less of the benefits of having twins than I used to.
Having twin infants was hard, but I am missing the days when they would just lay on the floor, or slowly crawl from one toy to the next. These days they are like a tornado.