The only reason is it's an Alienware so it may be nicer than most things.
But for 700 I would build my own from https://www.reddit.com/r/PCMasterRace/wiki/builds bit since yours has the OS, display and keyboard+mouse, it's an OK deal. Not outstanding but OK.
I apologize in advance for my wall of text. A coworker of mine bought a new computer and is looking to sell off his old one. I wouldn't mind upgrading to help play my games but lack an understanding of worth. Below I've listed most of the information he sent me. He's asking $700 for tower, no accessories. Is this a fair deal or is it outdated?
Alienware X51 Base
16GB Dual Channel DDR3 at 1600Mhz (2x8GB)
NVIDIA GeForce GTX 960 with 2GB GDDR5
WLAN Card DW1550 Driver
2TB (64MB Cache) 7200 RPM SATA 6Gb/s
Matte Stealth Black with Dark Chrome Accents
4th Generation Intel(R) Core(TM) i7-4790 processor (8MB Cache, up to 4.0GHz)
System BOOT for Windows, AW51
700 GPU-powered desktop
Alienware 330 Watt Power Supply