Honestly, I've been watching since the beginning (if I remember correctly, I screened the first two seasons on home video in a binge, and then started serially viewing on television), and it fairly quickly turned into one of those programs you enjoy but kinda/sorta hate to admit. This isn't to imply that it's an inferior program in any respect; the production values are very solid, and the big cast -- young and younger -- all turn in affable work in the Apocalypse drama.
Still, I have to admit that Season 3 just wasn't all that interesting plot-wise.
On more than one occasion, it felt a bit clunky, almost as if there was some behind-the-scenes tensions and/or creative developments not everyone was perfectly comfortable with handling, and a fair share of the action had series centerpiece Eliza Taylor (as the plucky Clarke Griffin) heading off on kinda/sorta 'vision quest' to 'find herself.' (My two cents: that's never a great thing for dramas, especially television ones.) Granted, it didn't last all that long, but then her characters (out of the blue) started experimenting with some lesbian yearnings; and -- although there were hints of some same sex attractions -- I never felt it evolved organically the way a good story would.
Thankfully, the writers never quite shoved it in the face of the viewers the way things happen on in the Greg Berlanti "universe of shows" (Arrow, The Flash, Supergirl, and Legends of Tomorrow); but it was awkward enough that I couldn't help wondering if network shenanigans led showrunner Rothenberg into homoerotic territory.
To the franchise's credit, no one has been spared from the ongoing carnage, and even a regular, semi-regular, or two have been felled in the sake of good storytelling. Not every death has created fascinating subplots to explore, but these young adults have certainly become the respectable 'Katniss Everdeens' for the TV generation. Plus, The 100 gives Henry Ian Cusick something to do; keeps Isaiah Washington around as a curious mentor; and banks smartly on the good looks of Paige Turco to keep older fanboys (like myself) mesmerized with beauty she's become.
Consider it a solid guilty pleasure, though don't look for all of it to make perfect sense.
If you're not watching, then shame on you. There's no time like the present to catch up (summer months are terrific for binging on DVD), and the future is yet to come.