A few of my thoughts about the episode that other people haven't covered...
First off, the title, "Unexpected," has got to be one of the biggest understatements ever.
The opening, with the loss of grav plating (with the added bonus of Jon floating around in his shower), was a good way to visually illustrate the beginning of their unexplained malfunctions. It was a lot better than just hearing someone list malfunctions, as is so often the case.
Maybe it's because I'm watching the rewatch episodes more closely, but I'm picking up on little things that I missed when I originally saw the series. For instance, in an earlier episode, T'Pol remarks that Vulcans don't use their fingers to eat food. In this epi we see Phlox eating pancakes with his fingers. Both are different from how humans would (normally) eat.
As someone else pointed out, the UT picks up the alien language almost too quickly. But I wondered how the aliens learned English so fast! Or was Trip speaking their language? There's the one scene at the beginning where Hoshi uses the UT through her communications console, and after that, everyone is speaking each other's language. I'll have to assume there was a portable UT somewhere on Trip, or the aliens had their own version of a UT.
Trip obviously is not feeling well on board the alien ship, which is a marked contrast from his earlier enthusiasm. But I wonder if he would have been so adamant about wanting to return to Enterprise if there had been someone else with him to share the experience.
The alien captain's line, "We have a good deal of experience with alien visitors," makes me wonder just how often their ship breaks down!
I can't make up my mind about Ah'len and the box of pebbles. She tells Trip it's just a "game we play," and yet it led to his pregnancy. Did she really think that because he was an alien that it wouldn't happen? Or was it just innocent? Then my mind went off on a tangent, wondering if safe sex for her species involves wearing gloves, and I had to back up the disc because I missed the next few lines!
Malcolm's got a dirty mind! And yet, after the comments about Ah'len's scales and the shared amusement with Trip, he wants to know about the aliens' weapons. That's dedication to his job.
I thought T'Pol went overboard in berating Trip for his condition. I'm a bit surprised Jon wasn't the one chewing him out, but you can tell that he's having a hard time keeping a straight face. I do think some of the crew reactions were a bit much, but the whole topic was played more for laughs than for anything else.
As far as Trip being pregnant... even at the original airing, I thought it was a unique idea (at least for what I've seen in science fiction) but I wasn't particularly thrilled about it. However, having had a couple of pregnancies myself, I was tickled by some of his reactions, especially the hormone-induced ones. The scene with the lift in engineering? Yep. Been in that overprotective/nesting mode myself. Scarfing down food like I was starving? Yep. Overreacting to things that shouldn't have caused me to blink an eye before I was pregnant? Yep. Even the deleted scene, with T'Pol carrying on about succulent sausages causing Trip to become even more sick to his stomach? I remember working a charity breakfast when I was pregnant, and the smell of sausage made me so queasy I had to work away from the serving line. A lot of what Trip was doing was cliched, but had a grain of truth in it. Trip's part was played over the top, but I could relate. I laughed out loud at the "working mother" line he had.
The crew of Enterprise is still learning lessons about being in space, and the lesson here is that even the most innocent action can have consequences.
A final note: Even though Travis and Hoshi's roles in the epi were much smaller than in previous ones, they still get something to do. Travis pilots the shuttlepod and gets to tease Trip with "I don't know. We are kinda busy." And Jon looks to Hoshi to explain the Klingon reference to Sto-Vo-Kor, which she promptly tells him is "the afterlife."