I missed Captain Scarlet the first time round in the 60s but through reruns it's always been my favourite Gerry Anderson show.
It doesn't have the goofball humour of his other productions and while humour isn't absent from the show (it needs it sometimes to keep from being too dark) it doesn't detract from the seriousness of the premise.
The new animated series is absolutely fantastic. Captain Black is a far scarier villain than before and Scarlet is a more human, more believable hero. I've heard some criticisms of the new theme but I think it is brilliant, exciting with a chilling edge to it, perfect for the kind of show that this is. My only complaint might be that it seems the voice actor for Scarlet can't seem to decide if the character is English or American, and sometimes the voice is a mish mash of both - is it just me or has anyone else noticed this?
But it doesn't detract from the show really - I love the changes they've made but please don't let Scarlet & Destiny get together (or at least note too soon) - will they / won't they adds a bit of spice.