This was the first episode that I thought wasn't all around great.
My big issue was the handling of Parasite. I've really like way they've handled political and social issues in the past, but this episodes whole climate change thing just didn't work for me. I think it is an issue that deserves to be addressed, but they did it here just didn't work for me. I was also disappointed they appear to be doing him as just a one off villain, he's a fairly significant villain in the comics, so I was really hoping he'd be available to pop back up occaisionally.
The stuff with Mon-El and the difference in his attitude and Kara's was pretty good. It felt pretty realistic to have a character with powers who didn't just instantly start using them heroically.
I was little surprised when we saw the alien he was threatening, I think his name was Brian, just walking around out in the city looking like an alien. I don't think we've seen that before, but I think it would be kind of fun if that became a regular thing, with random aliens just walking around out on the street, or in crowd scenes.
James as Guardian was really cool, and I liked the way they handled his relationship with Winn. It was nice to see Winn getting to do more than just sit as his computer.
The whole coming out thing with Alex seemed to be really well handled and, from the perspective of a straight person with no first or second hand expedience with the situation, seemed very believable. I was sad that Maggie turned her down, but her reasons made sense.