There are only few laptops capable of playing up-to-date games on high settings. And they are expensive.
Laptops generally arent designed for gaming, but for office use.
If you want to buy a laptop for gaming, you have to consider that you will have to pay more money for less performance. Your gain would be mobility and less power consumption on the other hand.
Personally, i would recommend a laptop for gaming only to the casual gamer. I find a desktop computer more convenient for long gaming sessions. Not only am i free to choose my pheripherals, such as keyboard and screen. If you add them to the purchase of a laptop, its gets very much more expensive, and you still save no space.
Anyhow, if youre going to buy one laptop, you should look out far a grafics card with dedicated grafics memory. Most laptop grafics cards use shared memory only, while there are some which use both shared and dedicated memory, or even dedicated grafics memory only, which is much better in performance.