I love my mission.
I am so grateful for the decision I made to serve a mission.
The reasons I am so grateful to serve a mission now, have only casual relevance to the reasons I, your friendly Stanford skeptical intellectual Mormon convert, decided to go on a mission. I see ourselves as very similar, so I hope this helps.
These are the reasons I am grateful now.
I learned how to love, serve, and get along with companions and investigators that were far, far different than me. Because I learned this, I was able to help people I would otherwise be unable to help. I was also far happier.
I learned the power of faith. Starting with, I realized the importance of my faith in choosing to serve, not understanding really what was in front of me.
Every baptism that I've had, or every person I've found that has been baptized, was a miracle. Not in the casual sense, but really, honestly, each one was a miracle. That means I've seen a lot of miracles in 22 months. My faith has grown a lot and I see a vision for my future life.
I now understand what my Heavenly Father wants from me. I understand what the gospel is and how it applies to me. I didn't fully understand this before.
I've felt my Heavenly Father work countless times through me. I've also felt countless disappointments, letdowns, frustration at companions, investigators, etc etc.
Minute mission rules (or culture) might frustrate at times. This is for two main reasons. First, you will be asked to obey things you don't understand. Second, we are both generally self-motivated and do things our own way; in contrast, a mission is very regimented. Other missionaries are not always as self-motivated, they might need the regimentation more, but you might need it too. Rigid schedules -- scheduled exercise, planning and study times -- helped me in some surprising ways to discipline myself.
Finally, whatever your course in navigating and obeying the rules, don't be frustrated at them. The rules are made for the right reasons; frustration wastes time, energy and the Spirit.
Doing the Lord's work is so, so worth it.