More an update than a sequel, BGC 2040 is a worthy addition to the Bubblegum Crisis mythos.
In this version all the characters have been redesigned, some radically. Most noticeable is Linna who went from being aerobics instructor to, ugh, an office lady. Sylia also got a major overhaul but I think this one is a real improvement. Plus, the implication that reason that all the Knight Sabers are female may have a lot to do with Sylia's sexuality adds a fun fan service element to things.
While the impact of changes is something for fan debate, I for one like most of them. They make the old world of original BGC, which is starting to show it's age after 15 years, seem more modern and relevant.
Style wise, the updated version of the Boomers, the Hardsuits and other technology looks really good. When you see it it's not hard to imagine that things like them could one day exist. One of the best improvements is to the Boomers. Back in the old days they were very stiff and Terminator-like. Now they seem more bio-mechanical which only makes them more creepy.
It's should also be noted that the animation on this is above average for a TV show, the voice actors are all wonderful and the music just kicks butt. I absolutely love the opening theme "Y'know."
In short, BGC 2040 is a good modern spin on an anime classic. Give this one a spin.
