My rMBP is a *piece of junk* at running games, completely worthless. But that is because laptops never were, and never will be gaming machines.
If you are like me, you're saying "I have an interest in games, but I'm not a hardcore gamer, so graphics don't matter." If that is the case, it is better to buy a PS4 and a normal Macbook. Or a cheap alienware PC desktop, and a Macbook Air. Or buy a used car, and an Xbox One. Or buy a desktop. A base, refurb Mac Pro is amazing. rMBP is truly the worst of both worlds: $3k for a gaming machine slower than an Xbox 360.
The cooling system is atrocious for gaming, or video editing for that matter. It doesn't result in an even decrease in fps, it creates a jarring stuttering to the fps which ruins the enjoyment of any game. Retina iMacs have cooling problems too, but at least the performance would be far better.
I bought a 15" rMBP in 2012, with 16gb ram and 1gb nvidia card, mostly for video editing but I assumed I could use it for gaming too. So you decide to game on this machine: first you need a laptop stand to cool it down and for basic ergonomic reasons (not tilting your head down 45 degrees every gaming session). Then you need an external keyboard because the laptop is on a stand. So now it is basically a desktop, with stuttering FPS and a fan that couldn't be closer to your face. If the laptop is now a desktop, why not just buy a desktop?
Retina is very nice when browsing the web, and that is it. Nothing uses retina effectively, and if anything games will be slower because you'll never play them at native resolution.
Recently I have discovered that my 2007 Mac Pro runs Skyrim significantly better than my 2012 rMBP. Not only that, but I can't even hear the fan, so I enjoy the experience much better even if it had the same performance. This Mac Pro can't even upgrade past OS Lion, and the rMBP "outperformed" it in every Geekbench benchmark before I bought it. A base Mac Pro from 8 years ago with 4gb of RAM outperforms this rMBP. That is not something you want to think about after spending $3k on a computer. Anyone who has the slightest interest in gaming should never buy a rMBP, unless your life involves constant traveling, in which case I'd rather game on my iPhone anyway.
This is a big load of crap. The rMBP runs games fine. You won't be running them at max resolution, but you can run them well. I've had the 2012 rmbp and was able to play BF4 in Bootcamp, WoW and Diablo 3, and the Witcher 3 under OSX. I have the 2015 2.5/16/1TB version with the m370x and I can run GTAV in Bootcamp on low/medium settings at constant above 60 fps.
Your 2007 mac pro, unless you upgraded the graphics card from the default options, is NOT better at gaming than the rMBP.