I need an Alienware EXPERT!! Performance questions about m14x r1

My model m14x r1(upgraded to 8 gigs ram).. I bought last year(2015).. Not knowing much about alienware at the time, and impressed by the lighting system, and thinking it was a up-to DATE gaming machine, paid 500$ for it, thinking it a good deal...      Heres the thing, generally its good for ALL older games, and even had allowed me to play a LOT of newer games, NOT at great framerates, but generally playable... Examples are mortal Kombat X(average 30 frames a sec, low settings), fallout 4(maybe 25-35 FPS, lowest settings generally), Shadow of mordor(maybe 40 fps on low settings) and even Mad Max(35 frames a sec)... 

Now, some of these games, looking at my specs, I shouldnt be able to PLAY THEM AT ALL!!  My card is the Geforce GT 555m..   May of these games are so far out and shouldnt be playable at all..      Especially considering how LOW my processor is considering what the requirements are(My processor Intel I7 2670qm, 2.20 Ghz(quad core hyperthead)...    So how can this be explained?  My MAIN concern is I really want to play the NEW DOOM, requirements for that are ALSO way above my system...  And is there anything I can do to SERIOUSLY improve my framerates for NEWER games on this model(and no, I cant buy another computer, Im very poor)..      Just looking for advice on HOW my alienware has been able to play these games that are far beyond my specs, and what I can do to further this...