Hello anon!
I’d like to break your message down, since there are quite a few ideas in there and you seem a little confused. (Disclaimer: it’s a complicated topic, and I am not The Ultimate Authority on Jewish belief. With that said):

I know ZERO things about Judaism and being Jewish (I’m a deist kinda)

There are many great places online to learn more if you’d like!

But is Judaism like agnosticism?

Judaism is a religion, but the Jewish people are also an ethnoreligious group. Not all Jews are religious or believe in G@d, and not all Jewish denominations require that you believe in G@d. However, for the purpose of this answer, I’m going to speak from my perspective, as an Orthodox Jew who does believe in G@d.

You say in judaism one can “wrestle with God and challenge him on things.” But if one doesn’t like what God does and thinks he does/says dumb things, why bother believing or worshipping them? Wouldn’t one be “better off?”

The way you worded this question is interesting. Rather than nitpick ( for example, wrestling with G-d doesn’t necessarily mean you think G-d does/says dumb things), I’m going to assume that the general question you’re trying to ask is: why would you believe in a G-d that you sometimes disagree with?

And the simple answer is: why would you believe in a G-d who you don’t sometimes disagree with? If all your beliefs match perfectly with your god’s, and everything lines up exactly between your own life and your belief system, you don’t have a g-d, you have a sock puppet rubber stamp-ifying your opinions. (Credit to @animatedamerican for inspiring that image, and for general input into this post.)

Ultimately, the world is a confusing place, and no belief system of any sort is ever going to make complete sense to anyone, whether from a logical place or from an emotional place. (I would, in fact, argue that not struggling with your belief system is indicative not of the inherent amazingness of your belief system, but rather of a lack of critical thinking on your part.) As a result, religion, and ultimately G-d, don’t have to make complete sense to you — there can be parts that you wrestle with, and despite those parts, your religion can still be the most fulfilling perspective on the world for you.

In addition, you can be religious without a complete understanding of G-d, much in the same way you can form relationships with other people without having a complete understanding of all human psychology. From a personal perspective, the perspective of a religious person, I know that G-d is beyond human comprehension, and as a natural consequence of that, I’m not going to understand everything that I believe G-d is telling me to do. In fact, a large part of my religious experience is taking the questions I have and trying to understand how to answer them, fitting the worldview I have from experience and from exposure to various philosophies into a Jewish understanding of G-d — not only that, but a large part of my religious experience is knowing that I will never in my lifetime understand G-d.  Besides, I know that I can never fully understand the natural world, and that means that if there appears to be a contradiction between something divine and something that I observe, it must be that I’m missing a piece of the puzzle, either from the natural side or in my understanding of the divine. The fact that my knowledge isn’t infinite doesn’t stop me from believing in G@d.

If anyone has anything to add, as usual, please do! You can ask me here, or reblog and add, or reply, or anything really!