1. How does the card stand on its own? Is it good, bad, or has potential? Is it worth playing?
Torterra can be pretty good on its own. Its first attack, Giga Drain, although it costs three energies (two with a DCE and a {G}), does 40, and you remove a number of damage counters equal to the amount of damage you did. This can turn Torterra into quite a tank, especially when you attach an Expert Belt onto it so that you can do 60 and remove almost half of the damage on you. Its second attack, Land Crush, although it costs four energies (three with a DCE, a {G}, and another energy of some sort), can hit for 80, which is pretty high damage, and put an Expert Belt on it and you can be hitting for 100 damage. Yep, Torterra can be very good on its own, and it can be worth playing.
2. What popular metagame decks is it used in?
As of now, Flygon/Torterra is the deck that uses this Torterra in competitive play. The deck won fame after it came in first place in German nationals in masters. The deck's strategy is too often use Torterra to attack a lot. You use the Lv.X to give it a boosted HP, and combine that with Giga Drain and an Expert Belt and you have one Pokemon that can become pretty hard to take down. Flygon is mostly there to give Torterra a free retreat thanks to its Body, but Flygon can still be a good attacker from time. Indeed, this deck does seem to be pretty viable in today's metagame.
3. What combos can you use it with? How so?
Obviously, I would use Torterra as it is being used in competitive play today. I would, in this case, use it with Flygon most of the time. As mentioned, Flygon will help solve the heavy retreat problem on Torterra thanks to the Body, and it can be used as an attacker from time to time to back up Torterra UL. As for Torterra UL, it would run the Lv.X so that it has boosted HP, and it can use the Poke-power when it falls behind. That's how I would often use Torterra.
Of course, there are more fun ways to using Torterra from what I noticed. Playing Torterra with Cherrim SF or AR works well too. With Cherrim SF, you make Torterra hit harder, and in turn, remove more damage counters off of it. With Cherrim AR, you can make Torterra turn into a real tank, where you can potentially reduce a lot of damage. I might even run this Torterra with Shaymin (Land) Lv.X so that Torterra can get a further boost in HP. Indeed, there seem to be so many ways to use this Torterra.
4. Give it a rating, and explain why you would give it that rating.
I would give Torterra a 4/5. Torterra can be a very fearsome tank, probably just as fearsome as Steelix Prime and Dialga G are today. Torterra has the potential to hit for a lot of damage, and it can really take some hits very nicely. When played with its Lv.X, Torterra turns even more monstrous. This, indeed, makes Torterra really good. The problem with it, however, is that it is slightly slower compared to other decks, so it may not necessarily catch up that fast. Still, Torterra is a type of attacking Pokemon that can really be tough to get through if you don't take it out on time.
5. How's the artwork?
I think it looks pretty interesting. Torterra really shows its fearsomeness in this picture. Indeed, I think this has to be one of the best Torterra artworks to date.