Transit has a lot of benefits for society. It gives transportation to the disabled, and those who have financial difficulty owning their own car. If enough people use it it can have a strong positive impact on the environment and on traffic. It's a social space and you can read while you travel. It uses little parking and so helps to save land and preserve the walkable scale of a city. It also has a lot of benefits to you in terms of saving money, especially if you take the plunge and get rid of your car.
However, since transit isn't profitable in most places where any significant amount of cars are owned (with the exception of things like airlines and inter-city buses), transit is subsidized. Therefore, it needs your help. Any time you pay a fare, you're making transit more self-supporting, and reinforcing its benefits to society and to yourself.
That said, transit has a lot of problems. In many places the service frequency can be soul crushing. Nobody, even the most die hard transit advocate, likes waiting around forever for the next bus. One of my main purposes in this blog is to point out that without the right kind of land uses (i.e. a densely built area), it is very hard to solve this problem. Nevertheless, you can and should complain. You should complain about uncomfortable seats, and the lack of bus shelters, and the lack of a real-time system that tells you when the next bus is coming. You should complain about rude drivers, and rude passengers. You should complain about the lack of grade separations in the new rail lines. You should complain about a society that isn't willing to step up and subsidize transit more.
In short, you should complain, but you should also support. Your feedback can help make things better, but without your presence and your money on transit, it's hard to imagine any real solutions. It's easy to just support or just complain, but it's harder to do both.