1. How does the card stand on its own? Is it good, bad, or has potential? Is it worth playing?
Looking at this card, Houndoom is a card meant to be on its own for it seems to be focused as a primary attacker. Houndoom Prime's Poke-power lets you flip a coin. If you get heads, the defending Pokemon gets burned. This can act as a potent Plus-power considering the fact your opponent flips a coin between turns to put damage counters on the burned Pokemon or not. Its attack, Dark Clamp, does 70, and the defending can't retreat during your opponent's next turn. Well, a flippy and a rather expensive attack that can't abuse DCE is quite a problem for this card since there can be better options compared to it. Overall, I would say this card is good on its own, but it doesn't have much potential and it is not worth playing.
2. What popular metagame decks is it used in?
As of now, there is no metagame deck that uses Houndoom at this very moment. However, if it were, I could imagine that it would probably be used as a straight Houndoom deck that focuses on Houndoom Prime as the primary attacker.
3. What combos can you use it with? How so?
I can't really see Houndoom being comboed with a lot cards. Blaziken FB Lv.X probably has to be the best partner since Blaziken's body increases damage from attacks done onto burned Pokemon by 40. Since Houndoom's power can burn, Blaziken can help it boost its attack so that it can be hitting for 110, or maybe even 130 with an Expert Belt attached (or even 160 if you can get three special darks and an Expert Belt on it). Now that could make Houndoom Prime one hard-hitting attacker as one may usually think.
4. Give it a rating, and explain why you would give it that rating.
I would give Houndoom Prime a 1.5/5. Sadly, Houndoom isn't really a good card to use right now. First off, as an attacker, its slow since it can't use DCEs, and the fact it needs three energies to attack means that many cards can out-speed it before it even attacks. Secondly, the Poke-power isn't that good since its flippy, and Blaziken PT is much better in terms like this since Blaziken PT can auto-burn no matter what compared to Houndoom's version. Yet, it could make a nice combo with Blaziken FB, but otherwise, that's about it. Houndoom is probably one of the worst Primes to date since there isn't anything really good about it.
5. How's the artwork?
The artwork is at least impressive. The darkened moon in the background certainly adds a sinister theme to this card, especially how Houndoom's face looks pretty evil in the artwork too. Hideaki Hakozaki did an impressive job with the art that's for sure.