Overall, the experience was fantastic. I highly recommend the immersion for any other language learners.
My Spanish improved (that's the point, right?). For me, the improvement was more about fluidity than new grammatical concepts. My professor was great; we passed many hours discussing topics as varied as politics, healthcare, archaeology, sports, and culture. I probably could have spent more time working on grammar, but for me, conversation was the most important.
We also had time for lots of other activities. We climbed a volcano and roasted marshmallows over lava, took a weekend trip to a lake, bargained in the local markets, took salsa dancing classes, participated in traditional culture events, and flew for a day up to northern Guatemala to visit Tikal.
But one of the best things we did is captured in the Spanish verb dominguar, which essentially means "to wander around aimlessly on a Sunday afternoon." Antigua (the city we were in) is an old colonial town still paved with cobble stones and situated around a large central plaza. Life really slows down there and we spent a lot of time simply wandering the streets, enjoying the sights.
I fear that I may have brought a friend (the internal kind) back from Guatemala. I've been sick for over a week now. I'm on some antibiotics and the doctors are running some tests. Hopefully I will see some improvement soon.
As you can see, the good certainly outweighed the bad. Here are some pictures from the trip.