Don't let the 3 first episodes fool you! The OVA takes a huge step to what it's suppose to be after those 3 first episodes. Really enjoyed the show when I watched 4-7.
I recommend to watch the original show before checking out the OVA sense it's story continues after and they spoil some story about the original show and they also tells you the personality of the characters and you might not want to know that until you know them by watching the original show.