Old dragon is old, but good nonetheless. Sure, it's a 7/7 flying for 8 and there are better creatures out there for that cost (Griselbrand comes to mind), but there's a big difference with this card: it's has 3 different types of firebreathing meaning that if you have nothing else to play in a turn, it's a 12/7 each turn (3 to pay for its upkeep, 5 for firebreathing). A 12/7 flyer isn't too shabby. However, you do pretty much have to tap out each turn for it to be bigger and it does cost 3 mana to live every turn, so it's a big investment. It can be worth it though.
Pros: Can be pumped up to be huge
Cons: Requires constant investment