I remember right at the beginning being told (and reading in the internet) that with twins the first year is hard but then it gets easier than it would be with a singleton. The theory was that twins will play together and therefore entertain each other. Well let me disillision you now, I've found this second year to be much harder than the first. Don't get me wrong there are definite highlights to this second year as well, but it has definitely been more work and less "selfish me" time and still twice as "hard" as it would be with a single toddler.
The first year is hard because of the lack of sleep with round the clock feedings and midnight wakings once they are suposedly sleeping through. But generally as long as the babies are getting fed, cuddled, have dry nappies and allowed to sleep they are generally content and "easy to please" and really in MHO not that much work. This all changes when they start moving about, suddenly you need to be making sure they are not getting into anything dangerous and have to provide a bit more on the entertainment front as they are no longer always asleep, but at that stage still not very hard to manage.
The reason I've found this second year so challenging is now they have more complex needs than just comfort, love, food and sleep. And unfortunately in a lot of cases they don't have the means to communicate these needs yet. This means multiple meltdowns when they don't get what they want, because we just don't know what it is they are looking for. They also are more mobile and into everything but have no sense of self preservation, this means when they are awake we have to be with them and can't do anything too involved chore wise due to the need to supervise constantly. THey also get bored very easily and so require more entertainment, the old myth that twins entertain each other- in our case it's rubbish. They steal each other's toys and copy each other but actual playing together doesn't come until later in their development (according to my milestone chart at about 3 years on average). This means we spend a lot of time mediating little wars.
Now again please don't get me wrong I love my twins and I wouldn't want to give either of them up but I would also like to set the record straight, twins don't suddenly get easier as they get older. They remain double the work of singletons but they also give double the joy and rewards! Watching them give each other a cuddle when the one is crying (only happens if the cause wasn't a toy war!!) or babbling to each other as seriously as though they were discussing world peace are very precious momoents and wouldn't be possible if they weren't both there.