Is Nvidia GTX 660 2GB a good graphics card?

It is quite a mid end GPU so it will run most modern games on high settings

Not too bad.
http://www.videocardbenchmark.net/high_end_gpus.html

Yes it is a perfectly capable graphics card of running both of the games, especially since it is a Alienware.

Minecraft does not so much depend on graphics card but the amount of RAM and you seem to have a reasonable amount at 8Gb. So Minecraft will run smoothly at high render distance and particle settings.

Its one of the better and most competitive graphic cards out there for the price… And its more than capable of running games such as black ops 2 and cod ghosts at maximum detail and resolution
I wouldn't call it a high end/performance card as that title is left for cards such as the GTX titan or the GTX780ti… However I would call it a mid to high end card and combined with the core i5 2320 and 8gb of ddr3 ram you can expect to run any current game at high detail settings at 1920x1080
the alienware x51 is quite a new gaming pc and is based around a small form factor case which is around a third of the size of standard alienware gaming pc, s… It also uses a power brick instead of a standard power supply which allow more components to be squeezed into the limited space in the case
also the x51 comes with the unique alienware lighting system which is all controlled via the alienware control center… You can have more than 8000 colour combinations and that's not all. There's also
1) AlienAdrenaline. Lets you set specific parameters for each game which can include overclocking
2) AlienFusion. Lets you control your systems power resources, so you can ensure your pc has the power it needs as and when
in terms of gaming well as I mentioned the x51 will run any current game at maximum detail and resolution, and it will probally allow you to run any forthcoming game for the next 3 to 4 years…
I hope this helps syed… Any questions let me know

Yes Very Good And Previous Model Is Also good