Historically, very few Ultrabooks have been good for gaming. Held back by the aging Intel graphics, not many can run Battlefield 3 at all, let alone without lag and at decent framerates.
The Timeline could change that. The 15 inch chassis isn't quite as well built as the similarly sized MacBook Pro, but it's quite a bit lighter and over £1,000 cheaper, so it shouldn't hurt your wallet too much. Incredibly, the Core i5/GeForce GT640M spec is pretty much the same as the Core i7/GeForce 650M in the MacBook execpt for the two CPU cores.
The backlit keyboard and mouse pad are excellent too, and unless you're gaming, the fans rarely kick in at all. The noise produced is so minimal, in fact, that any hard drive thrashing can be quite distracting - although it's good to know that inside the Timeline there's a 20GB Solid State Drive to help with boot speeds.
Unfortunately, the 1366x768 screen is just too low resolution for a laptop of this size. It's not awful quality, however the colours do suffer, as does the image sharpness and available space on the desktop.
Not all is bad, as gaming at this low res doesn't require much power. That GTX 640M can almost get Metro 2033 running fine at top tier-ish detail settings. Almost.
Given the price, it may seem in bad spirit to point and giggle at the screen, but this is exactly the kind of false economy you'll be paying for in the long run. Laptops with Retina quality displays and touchscreens, eIPS will be here soon, and this laptop will become old rather fast.