Oh god, there were SO many surprises...
For one, I was really surprised first at how hard it was to be a guy, and then how easy it was, if that makes sense. I had a weird time at first because I dove headlong into hypermasculinity, and was upset because I couldn't express my feelings anymore or talk to others about theirs. I even had some second thoughts about transition. However, it was kinda funny- as I got further along in transition and really settled in to my new roles and relaxed on trying to be more masculine than I really am, I realized that I can still be my same old self with my friends and family, even if I have to really act it up sometimes around groups of men. I was almost a little surprised at how close I got with all my guy friends, too- I always kinda assumed I'd be closer with them as a girl than as a guy, but it ended up being the opposite, and a lot of my friends that never really talked to me about that much personal stuff really started opening up to me.
Another surprise: people were WAY more accepting of me when I swear, which I think is kind of ridiculous, but that's neither here nor there.
Another one: I became really really feminist. I was never *not* feminist pre-transition, but transitioning really brought to light all the BS that girls have to deal with- I'll often tell people that the quickest way I could tell if I was passing or not was if I was being treated with respect, and that's really upsetting, knowing that women go through that kind of stuff all the time.
Last one: I finally came to accept my bisexuality! I'd known I was bisexual since 6th grade, but as time went on, I convinced myself I only liked girls because it made me feel more masculine, I guess. But when I got comfortable with being a guy, I realized that I didn't just like girls at all, and was finally able to be myself, really. It was pretty cool.