Just like any other computer, what matters most is the parts it's made out of, not who made it.
There are Dells that are that built quite solidly, and there are Dells that are not. Same as any other brand.
For a gaming laptop you're looking at the same things you'd be looking at with a gaming desktop:
- Processor
- RAM
- Graphics
A solid state hard drive is nice too, but laptops that include mounts for them tend to be on the pricey side.
Generally an i5 with 4GB of RAM and a discrete graphics chipset (not an integrated intel chipset) is going to do fine. And there are any number of manufacturers that make that.
In general Dell, Lenovo, and Asus make very solid laptops. But you always have to do your homework ahead of any computer purchase.
Also steer clear of Windows 8 if you can; at least for now. Don't touch new Windows until the first service pack so you're at least not paying them to beta test their product.