Is it a bad thing to have too much rock? Why?
Well there's a couple reasons.
The first, and most logical, is that you are greatly reducing the amount of room that you have for fish and inverts.
The second, and more important, is that there is great potential for dead-spots in your tank: areas that there is no water flow where pockets can form of proteins, nitrites, nitrates, ammonia - all kinds of nasty stuff. With your rock configured the way it is, you're going to need a good number of power heads to ensure sufficient water flow.
What kind of fish are you thinking of putting in there because, again, keep in mind that if your 60 gallon tank has that much rock in it, you realistically will only have around 40 gallons of water (rock does take up volume).
Just my two cents - might want to remove a few of the bigger chunks of rock. It'll give you more flexibility in terms of arrangement, and also let you fit some holes in there for water flow purposes.