First of all, I'd like to add that HBs' decks aren't random. They're 144 different rigged decks. They're a lot, and it looks like random cards, but it ain't.
Half bloods are just "worse than" in every single aspect (now even more with the upcoming of Arena).
- They're worse than FG's in the rewards, for they have, half -or less- upped decks. So in the spins you have to match the 3 spins between a DOUBLE amount of cards. This also makes even the unupped cards harder to get from them. The solution to this would be either making the spins be 2/3 of unupped and 1/3 of upped; or making any kind of card be either fully upped or unnupped (like 6xWerewolf -upped- 4xAntimatter -unupped-, etc, not 3xWerefolf, 3xLycan, 2xUpped AM, 2xUnupped AM), this would lead to simpler spins, but would also mean a total rework of all 144 Half Bloods. They also suck at being predictable, so you can't make so easily a reliable HB deck, being easier to farm FG's.
- Even though being 144 decks, they're now worse than Arena in that they're less random. So, if you want unpredictable fun, just go to Arena. Also, the rewards there are better. I don't mind HB's losing some unpredictability by making every deck somehow oriented to a decktype or whatever.
- They're worse than AI3 in that they're harder, so the matches last longer, and it's quite too easy to farm AI3's, so you're sure to win >90% with LOTS of differents unupped decks, and waaaay faster than farming HB's, so the difference in rewards ends up being worse too. Also, the spins again.
Huh, I don't see how to fix all this, or what niche could HB's occupy, but I guess the upped/unupped cards thing should be solved, for it's the easier solution. I personally prefer the most complicated one, of making every set of cards either upped or unupped, but the other option could work too.