Pros
If you're looking for a long career in car sales there's probably not a better place to be. It is quite safe from downturn because PAG is a gigantic machine backed by Roger Penske, a financial shark and great businessman. Additionally, depending on brand, there are so many brands that the manufacturers generally love Penske owned dealerships, which is good for inventory. There are many dealerships to transition to, lots of potential for upward mobility if you politic and play the game.
Cons
It is VERY corporate. It is also very "old-school". The organization is slow to make change, because everything needs to be "approved." You are just a number. Management will never give you direct feedback, it will always feel like you are at arm's length from your bosses.