I've been to a few ballparks, am a regular visitor to Shea and Fenway. I was dumbfounded at my first sight of Petco. But what waited for me was even more incredible...
Petco prices are phenominal - if you want to have a seat behind the plate, you can pay almost half of what you pay at Fenway and that's if you get seat at Fenway. I didn't try the upperdecks but I did check out the Western Metal Building from the left field line where you become literally part of the field and a fence stopping you from leaning into the field of play. Also, you can go up to the 3rd level of the building and watch the game from the balcony of the bar & grill for no extra charge other than a $5 ticket! Same with the left field line.
Left field bleachers feature the infamous "Harry the Heckler" who heckles opposing teams' left fielders. He is harmless, does not drink at the ballpark, loves kids and if you ask nicely, will get a ball for your kid as the players throw them up to him. Right field bleachers feature Franklin, the "K guy from Qualcomm" who is an usher who used to put up the Ks for strikouts. His whole section is loads of fun and makes your experience that much better.
Because the concourse is open to the ballpark in most areas, you can walk around and still view the live action. You are not required to be cemented in your seat.
Another feature in right/center field is the sand pit which is only available for kids but it's right up against the fence of the ball field. So parents buy bleacher seats for the sandpit and kids can play in the sandpit. OR you can spend a whole $5 per ticket and sit in the "Park at the Park" which is this hill of grass above the right/center field bleachers overlooking the ballpark. This allows you the experience of watching the game as if at a Little League game and on the back side of the "batter's eye" is a huge monitor to see the action up close.
Bottom line, a group of people or family can enjoy the baseball experience at its best for a great price and even bring in your own food.