Alienware is too expensive for how weak of a computer they usually are. Macs on the other hand I find much better than a PC for graphic and artistic endeavours.
For video games I would have to say either the Halo series or Transistor.
As for films, I think my favourite would be Tron Legacy (don't get me wrong the actual film wasn't very good, but Daft Punk produced one hell of a soundtrack).
I would personally recommend Counter Strike: Global Offensive over CoD or Battlefield, it does however have a bit of a learning curve. Once you get into Counter Strike it will entertain you for hours.
So is it just giant monsters, like Godzilla etc, or is it monsters from movies in general, because if you just search up monster movies it includes everything from Alien to Dawn of the Dead.
In all honesty, there isn't really a lot of free to play sandbox games, but there are some quite cheap ones, that can be found on Steam. E.g. Space Engineers.