Moltres MD is somewhat more interesting compared to its other Legendary Bird counterparts from MD, simply because it pretty much combos with itself.
HP of 100 is great for a non-evolving Basic, weakness to Water is bad (especially for the x2 weakness, despite not being an SP), and 2 retreat cost is somewhat annoying to pay.
Basically, Moltres functions as a late-game attacker in fire decks. By the use of Flame Charge, it can be powered-up in a pinch. Most Fire attackers discard Fire Energy like there's no tomorrow (Infernape 4 LV. X, Magmortar LV. X, Blaziken PL) so it is not difficult to have those needed energies in the discard pile. Of course, it is also plausible to use Felicity's or Volkner's if you want to discard immediately. The downside is (and the reason why it is not used much) is that the power works on a flip. That might be tolerable, but upon the disadvantage of being a coming-into-play Poke-power as well, Flame Charge just seems very out of place to use in the competitive matches. A Power-Sprayable attack that relies on a flip is really bad today, and unfortunately, Moltres does not have the luxury to use Poke-Turn as a failsafe measure.
Scorching Wing is pretty much your usual powerful Fire attack that discards the energies. However, 100 for 3 with the discard is pretty weak nowadays and if not for Flame Charge, the attack would be pretty much unusable.
Moltres can be a nice tech in Fire decks, particularly ones that can manipulate energy on the board (like Charizard G LV. X) or with the aid of Energy Links. As a main attacker, it is pretty much outclassed by fellow Basics Infernape 4 and Blaziken FB in terms of speed and Energy efficiency. I guess the rule of thumb would be, if a Pokemon needs too much energy to perform an attack and at the same, does not have enough lasting power to use that attack before it is KO'd (which is very common for Legendaries and non-SP, non-evolving Basics), it is probably not worth it.
Modified- 5/10 (the power would have been great if not for the flip)
Limited- 7/10 (a decent energy accelerator here and Scorching Wing is a great late-game finisher)