The RAM is also necessary to load the games executing files. 4GB DDR2 RAM is a standard for gaming laptops these days. Any current game these days don’t need more RAM than that but if you have some money to burn and want to be prepared for the upcoming games, you might get yourself more RAM. You can also go for DDR3 RAMs : they cost more and provide faster speeds.
For the immersive gaming experience look for bigger screens with higher resolution. Nowadays 20+ inch screens are available but if you take my advice don’t go for screen more than 18 inch because then you have to compromise on the portability of the laptop. On the other hand, a screen less than 18 inch won’t give you the perfect gaming experience as you’d want. Also look for true HD resolution screen of 1920 X 1080 p for better details. You can also watch full HD movies without rescaling on your laptop.