I don't think that Seichin was that hard for me to learn. Like Dana said, a lot of it is from your other kata. However, some moves in Seichin are tough, and will feel very wierd for awhile. Give them time, practice those movements again and again, and eventually they will become natural for you. But don't sweat it, it's not too tough.
Also, like Dana, Seichin is one of my two favorite kata.
Have fun, keep training!