These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Kyle XY
Anvilicious: "Free To Be You And Me", which delivered a rather heavy-handed Aesop about homosexuality, including having all the main characters organise an alternative school dance for gays and lesbians to go to, having Josh learn a valuable lesson and having Jerk Ass Charlie behave homophobically.
Complete Monster: Cassidy in Season 3, after the revelation he killed Sarah and his actions in the finale.
Germans Love David Hasselhoff: Kyle XY gets more love in Spain than he does in the States. With an average of three million viewers per episode in Spain (huge in European TV), this show remains a fundamental program for its broadcaster.
Ho Yay Shipping: Kyle and Declan (dubbed in-universe as "Keclan" by Hillary). When the two have a falling out in Season 2, people speak about it as if they had broken up.
Inferred Holocaust: In the middle of Season 2, Kyle and Jessi cause a city-wide blackout. No mention is made of the inevitable casualties that would have resulted of this (car crashes, etc).
Mary Sue: Kyle. Borders on Deconstruction, as most of the characters are well aware of Kyle's utter perfection, and one character got him drunk just because he wanted to see if Kyle had any flaws. It still doesn't work.
And again, a deconstruction of the ideal 'perfect son'. The other teenagers are depicted as heavily flawed, but not without their good points. Despite Kyle's so-called utter flawlessness, the show goes to great lengths, particularly during the first half of season one, to demonstrate that raising someone like Kyle is no easy task.
Nightmare Fuel: At the end of "The Future's So Bright, I Gotta Wear Shades," Kyle learns he can manipulate water, and immediately proceeds to pull Jessi onto the roof as she attempts to jump off. While his intentions were honorable, there's really no getting around the fact that he just learned...bloodbending.
Kyle: The human body is 50% water. (cue Josh's "holy-shit" face)
Seasonal Rot/Sophomore Slump: Season 2 was the weak link in the series, spending more time on the tangled mass of love triangles and teen relationships than Kyle himself, and failing to provide a major villain. It got better by the time of Season 3, which is probably the best season in the series.
Ship-to-Ship Combat: Just go onto the boards and be prepared to be met with tons of threads documenting the all out war between the Kyle/Amanda shippers and the Kyle/Jessi shippers.