Ensemble Dark Horse: Ben/X5-493 only appeared in one episode, but proved popular with the fans and with the writers, so much so that they decided to bring Jensen Ackles back as his clone, albeit with a very different personality.
I Am Not Shazam: Occasionally one finds people on the internet who think Max goes by the name "Dark Angel". She doesn't. It's a reference to her dark past, dark complexion, angelic features, and job as a bike messenger.
"Angel" because from the pilot onwards she becomes a (beautiful female) hero to the downtrodden, and "Dark" because she has bleak past as a government-engineered super-soldier/assassin, and a somewhat dubious present as a part-time cat burglar, and not of the Robin Hood variety.
The angel - messenger connection is made explicit in "Art Attack" when she prevents a man from committing suicide and introduces herself as a messenger, which he thinks means "of the Lord".
Many people on forums confess to only watching for Jensen Ackles. Unfortunately, this usually means they watch only "Pollo Loco" and Season Two, and thus don't appreciate that Season One is also good.
Both Sky1 and SyFy in the UK (when it was still Sci-Fi) implied in their trailers that the main reason to be watching was Jessica Alba. This proved to be the case for a lot of people (and unlike Jensen Ackles, she appears in every single episode).
The Problem with Licensed Games: A beat-em-up game was released for the PS2 and Xbox in 2002 after the series was cancelled. While the voice acting is decent, the game is repetitive and has some major problems with its stealth mechanics.
Michael Weatherly, who played Logan Cale, would later be cast as Special Agent Anthony DiNozzo on NCIS, a role he held for thirteen years.
The Scrappy: Asha was another one of Logan's agents introduced in the second purely to drive a romantic wedge between Max and Logan. That of course pissed off the shippers. Meanwhile she had no interesting personality or skills of her own.
9/11 happened between seasons, and suddenly, portraying the government as evil, portraying the police as evil, or portraying America as evil could all lead to spectacular backlash. All those aspects had to be toned down, even though they're all necessary in a Cyberpunk setting.
Max and Logan admitted their feelings to each other but the writers wanted to keep the dramatic tension, so Max was infected with a virus that kept her and Logan from touching. Instead of the flirty Will They or Won't They? of the first season, the audience got romantic Wangst.
Max and Original Cindy's social lives disappeared along with a large part of their social circle. Instead of hanging out with their friends and dealing with dystopic city life, Max spent all of her time getting Alec and Joshua out of trouble and whining about it. Great for Jensen Ackles fans, bad for everyone else.
Most importantly, the cheese was gone, along with the Totally Radical. No more stories about Max going into heat and having to distract herself, or making enough money to bribe the police, or rescuing her friends from Japanese gangsters. Instead it was all about collecting lost transgenics, which were too serious and low budget to be exciting, and not fun enough to make up for it. Not that the show wasn't about finding lost transgenics before, the first season was about Max trying to find her family, but she did other stuff as well.
The Woobie: Joshua. Between having to kill his deranged brother Isaac to protect Max and Ames White murdering his girlfriend Annie, it's a wonder he's still well-adjusted.
For the Band
Broken Base: A lot of it between their first two and latter two albums, but the main points of contention are Don Doty vs. Ron Rinehart and the general decrease in brutality after Darkness Descends.
Face of the Band: Gene Hoglan. Interestingly, he wasn't a founding member and didn't even appear on the first album, but once he joined, he seems to have become the band's dominant force almost immediately.
Sequel Displacement: It's not by any means the best (neither in fame or in quality), but there was indeed an album before Darkness Descends. Not helping matters is that one of the songs on the album was recorded again for Descends.