I don't like to talk too much about it, for fear of sounding preachy, but since I was asked....
I do Judaism. My mother raised our family in some traditions during my childhood, then these faded away in my late teen and university years, as I lost interest in the spiritual side of things. After graduating, I slowly decided to re-investigate, so now I am solidly in the Jewish fold again. Probably in what would be considered the "Conservative" denomination, which is like a "middle-way" between the strict rules of Orthodoxy and the liberal individually-based Reform movement. The theology in Conservative Judaism can actually be pretty liberal, but the practice of the customs and laws is supposed to be somewhat rigid in contrast to that. Strangely enough, this leads to the "why am I doing this when I don't necessarily believe in it?" feeling that pushes many people out of religious practice. Judaism has some interesting (not satisfying for everyone) answers to this:
It is more important to practice Judaism than to believe it. Why? Because doing good things is always a positive for the world, whether or not you realize/understand that it's a good thing. Actions speak louder than idle beliefs, I guess? And this is one of my favorite reasons to keep practicing Judaism; essentially, it is the pursuit of doing good things and being a good person (although some of the logic behind the rules is not straightforward, of course).
There is weight in the history and the traditions themselves. At least for the individual, this can be fulfilling to connect to generations of ancestors stretching back several thousand years, and in a sense appreciate what it meant to them. When I think on the fact that many of them risked death rather than convert to other religions when pressured, it gives me a great feeling of resilience and perseverance. That this custom only exists because, again and again, generation after generation, some made the often perilous choice and insisted to continue the line into the future.
Study is probably the primary form Jewish "devotion" takes. When Jews are "devoted" to their religion, this usually means they are studying the Bible and the writings and discussions about the Bible. It's considered one of the highest forms of observance, to try to become closer to God and to understanding what God intends for us. So I think as long as we are pursuing and studying, we are on the right track and not the wrong track. Maybe we are not doing well, but at least if we are improving, we are learning something and becoming better people...
Not all Jews would agree on these reasons, but they seem pretty widespread and common enough to say "most" would agree, especially most in Conservative Judaism.
In practice, however, I do tend to interpret the way I think makes the most sense, if a tradition does not seem right. But often I have found, as I learn more about orthodox, historical reasons for many customs, that the reasoning is sound and I just wasn't informed enough to understand at first.
Many of the practices involve repetition or routine, which again is something that can turn people off to religion. First of all, I often modify these to make my own routines, but based on established historical structure (kind of

). Second, I think having the structure of routine itself can be a positive, too, because it reinforces the idea that Judaism is a commitment--like a relationship with a husband or wife, this is a committed relationship with God. Relationships require effort, have ups and downs, and may not always be purely fun and fluffy, although they have great moments that are moving. I kind of like that sense of dedication that motivates me to keep going.
Also, in my mind, it's a "most logical" form of religion. Being pure monotheism, it reduces any extra, unnecessary concepts about God down to the simplest view. Why say that there are gods in each tree and each river and each rock? Couldn't they all be considered of one form, and couldn't that form be considered one God? Or why say God has different persons? Aren't those persons complicating aspects of the same one God? They may not even be wrong, but they are ultimately unnecessary (as I see it) when all boiled down to "God or not God". This is why I think, besides Judaism, the only real alternative for me would be atheism. Or well, perhaps Islam, which is pretty monotheistic as well.
Plus, there are so many good holidays and they're all meaningful and thoughtful.
No offense was meant by any of the above. I only tried to explain my mind's rationale for beliefs I hold.