1. How does this card stand on its own (analyze the HP, attacks, Abilities, etc. of the card)?
This pokemon tanks pretty well with 180 HP, although the HP is par for the course with the new EX pokemon. The retreat is high, but is also fairly typical for the pokemon's EX status. The attacks are interesting, costing more energy than the damage is worth, but having abilities that might at least make them playable. The first attack would have been better if it cost a single fire and if the second attack was a fire and two colorless. The energy requirement makes acceleration a must to be useable, thus hindering its otherwise decent stand alone stats.
2. What role does/could this card have in the metagame?
It could serve as a tank in google variants, especially since it has an energy recovery engine in a deck that can only use Flower Shop Lady for the task. It could also be a tech in Reshiboar, though I think Reshiram EX fills that niche better.
3. What cards, if any, does this card combo with?
Emboar is a local choice given that the acceleration will help compensate for the cost of Entei's attacks. Ninetales also makes sense since Entei's second attack acts as energy recovery, and can be then used to charge up backup attackers on the bench (Reshiram being a good example Volcarona can also increase the damage output of the burn status caused by Entei, making the first attack fairly decent for two energy if the opponent can't switch out. Vileplume could be used to prevent the switch, and this may indeed see some play in google decks, especially with Reuniclus to move damage counters off Entei, but the slow energy drops could be problematic. For similar reasons to Eelektrik or Typhlosion, Junk Arm can be used to discard energies that can then be used to attach with Grand Fire.
4. Give it a rating (out of 10), and explain why you have given it that rating.
I'd say Entei is a 5/10 card. It has cards that can certainly make the effects of its attacks better, especically Volcarona, but the problem comes in with the simple fact that the energy costs warrant some acceleration to be really viable, needing a stage 2 in Typhlosion or Emboar in all likelihood, in addition to the stage one in Volcarona to get the burn to work. Worse still, the opponent can easily switch or retreat out of the status condition, so if they win the initial flip, the effort is wasted. Pair that with loses two prizes on a KO, and you have an interesting, but ultimately not metagame, EX card. (I really rated this too high the first time)