1. How does the card stand on its own? Is it good, bad, or have potential? Is it worth being played?
This card was one of the most hyped up cards in the current metagame, and with good reason, it could possibly dominate any deck, provided the deck it's in is fast enough. However, it could still carry over into the newer, slower metagame with Black and White coming out, with the new rule sets. Until it gets rotated out, it will probably be the biggest metagame changer since SPs.
2. What popular metagame decks could it be used in?
Lostgar is the first thing to come to mind, but it could probably handle its own in any zoning/sniping deck, 130 HP, being able to snipe, and its Pokebody isn't something to scoff at. You can't, like most cards, shoehorn it into any old deck, I'm sure.
3. What combos can you use it with? How so?
Mr. Mine could help bring this into play, especially against Gyarados if they haven't discarded all of their Magikarps yet. If one Gyarados gets knocked out, however, it's automatically game-set-and-match if Gengar is the active Pokemon. Hurl Into Darkness can also work well with Seeker. You know when you play one something important's going to be pulled back, most of the time Uxie, or any other draw power card. Easy pickings. Lost World is also a great card to have with this one, if it isn't a main card in LostGar already, well that'd be silly.
4. Give it a rating, and explain why you have given it that rating. You can also rate the card by rating the thread itself (out of 5 stars).
4.5/5, that x2 Dark weakness isn't totally avoidable, but it's still not raising any red flags. Yet. If one were to look at the Player's Sandbox section of the forum, one may see at least two threads talking about "how to beat LostGar".
5. How's the artwork?
The close-up shot with his tongue hanging out makes him look mischievous, but at the same time, the glint in his eye and the swirling colors around it give it a sinister appearance. The art work alone could send most decks running with its tail between its legs, if it had one. Or legs. One of the more appealing primes to look at, without being boring.