It's a big deal. The dissatisfaction tends to be different for young men and young women. Women, for instance, tend to be more interested in romance. As much as this appealing, many young women fear that losing their virginity is equivalent to losing their reputation. The situation is a bit different for guys, in part because most young men see their first time as a more positive experience.
Young men tend to feel a stronger sense of achievement after losing their virginity.
But even guys can feel disappointed. They tend to think about sex in more erotic than romantic terms. A guy might have unreasonably high expectations for the first time. We're all bombarded with sexual messages from TV shows, movies, ads, and so forth. At the same time, adults tend to stammer and blush whenever sex comes up in conversation.