Wait a second. You bought an Alienware? I seriously reccomend you return it asap if you can, and order a proper rig online, for way less money. Alienware is overpriced crap.

Some more classic games, not sure if you can get them working on Windows 8/10 now.
I could go back further to older abandonware or niche games?

Here are my favourite series:

Age of Empires series (2)

Civilization series (II)

Command & Conquer series (Red Alert 2)

Commandos series (#2)

Grand Theft Auto series (2)

Need for speed series (-)

Maxis sim series (The Sims, SimTower!)

Portal Series (2)

Rollercoaster Tycoon or Theme Park series (TPW)

Theme Hospital (-)

Tomb Raider series (OG)

Trackmania series (OG)

Warcraft series (2)

... and play some Wolfenstein3D/Doom or UT99/Quake3.

Remember if it has a 2 it's better

If you really want some classics
X-com: ufo defense
Half-life 1
Starcraft [1+brood wars]
Worms 2
Return to monkey island
Command conquer red alert.
Loom
Classics every one of them

Civilization V. But you need the complete edition. Otherwise the game sucks.

The diablo series,including the modified versions and the dungeons and dragons style games,(Baldur's gate,planescape torment,neverwinter nights.) I also recommend trying out emulation for any classic console and arcade games you missed,saying that may be against the rules here.

Action-Adventures: Alan Wake, Alien: Isolation, Assassin's Creed series, Batman: Arkham Asylum + City, Beyond Good & Evil, Darksiders 1 + 2, Deus Ex series, Dishonored, L.A. Noire, Mark of the Ninja, Overlord 1 + 2, Prince of Persia series, Psychonauts, Resident Evil series, System Shock 2, Tomb Raider series

Action games: Bully, Dark Messiah of Might & Magic, Dead Rising series, Dead Space 1 + 2, Devil May Cry series, Forsaken, GTA series, Hitman series, Mafia 1 + 2, Max Payne series, Mirror's Edge, Sid Meier's Pirates!, Splinter Cell series, Thief series

Adventure: all LucasArts adventures (Day of the Tentacle, Monkey Island, Indy, The Dig...), most Sierra adventures (Gabriel Knight, Space Quest, Larry 1 - 7, King's Quest...), most Telltale Games adventures, Blackwell series, Broken Sword series, Deponia series, Discworld series, Dreamfall, Edna & Harvey series, Life is Strange, Secret Files series, TBoUT series, The Longest Journey

FPS: Battlefield series, BioShock series, a few CoD-games, Chronicles of Riddick: Escape from Butcher Bay, CounterStrike series, Crysis series, Doom series, Far Cry series, Gears of War, Half-Life series, Left 4 Dead series, Metro series, No One Lives Forever 1 + 2, Prey, S.T.A.L.K.E.R., Star Wars Jedi Knight series, Team Fortress series

Puzzle games: Antichamber, Braid, FEZ, Portal series (Mods included), The Stanley Parable, The Talos Principle, Trine series

Racing games: Assetto Corso, Burnout Paradise, DiRT series, F1 series, FlatOut series, GTR series, MotoGP series, Need for Speed series, GRID series, Project CARS, Rocket League, Trackmania series

RPGs: D&D games (Baldur's Gate, Icewind Dale, Neverwinter Nights, Planescape Torment), Diablo series, Dragon Age series, Fallout series, Gothic/Risen series, Jade Empire, KotOR series, Mass Effect series, Pillars of Eternity, The Elder Scrolls series, The Witcher series, Ultima series, Vampire 2, Venetica

Space Sims: DarkStar One, Elite series, FreeLancer, FreeSpace series, Star Citizen, Wing Commander series

Strategy games: Age of Empires/Mythology series, Anno series, Civilization series, Command & Conquer series, Company of Heroes, Dungeon Keeper 1 + 2, Homeworld, Sim City series, SpellForce series, StarCraft series, Total War series, WarCraft series, World in Conflict, XCOM series

other: The Sims series, Minecraft, World of Warcraft, Dota 2...

No reason to make him feel bad about his purchase...he clearly has money to spend or else he would have looked for a cheaper option or bought a PS4 or an XBO.

What kind of games do you like to play?

RPG: Baldurs Gate II enchanced edition
Pillars of Eternety
fallout 1 & 2

FPS:
while you can get most of them going back to doom by looking around - if you want multiplayer at all I suggest sticking to one made in the last 2 years - pick your flavor and go have fun

Strategy:
Civ V
(Civ IV and III are good also - the newest one is still kind of bland honestly)
Total War series

ARPG:
Diablo III
Path of Exile (ftp)
Torchwood I and II
marvel Heroes

MORPG:
World of warcraft
Everquest I and II
Guild Wars 2
RIFT
Neverwinter
Dungeons and Dragons Online
Lord of the Rings Online
give them all a try - they all have a 'try without spending a dime' mode

Action:
Tomb Raider (if you haven't played it yet - the new one is great)

Simulation:
Car Mechanic 2 (honestly it's disturbingly addictive)

Strategy 4x (you many not know this as it's not a console genre)
Sins of a Solar Empire
Starcraft 2
Warcraft III

Adventure:
Deponia the complete series
Kings Quest I - VII
Heroes Quest I-III
etc.

Great games from the past that you may or may not have an easy time tracking down (and frankly in some cases have a hard time running well on modern hardware without taking time to emulate older machines):

Freespace2
SSI Gold box RPGs
Ultima I-VII
Tex Murphy series
Gabriel Knight series
Planescape : Torment
Wing Commander series
Diablo 1 and 2


Finally - almost any game that has it a console in the past 8 years can be found on PC - that being said you can peruse 'game of the year' awards and such for gems.

http://www.pcgamer.com/the-pc-gamer-top-100/

This should have a few that interest you in that list as well

I do want to add one thing that a person new to PC gaming might not know about:

Unless you have money to burn, wait until sales to make the bulk of your purchases. Especially the annual sales, where just about everything is discounted.

Between places like Steam, Green Man Gaming, and GOG.com, you can save 50% or more if you buy during sales. Stuff on your wishlist, that you don't have to own right now, can wait. Sales are the life's blood of PC gamers. Just keep checking. Like, right now, GMG has Far Cry 3 for $9.99 on sale.

First off, I'm just gonna say you made a mistake going with Alienware. Have fun with Dell's customer support if you ever have any issues ever. I'd highly recommend you build it yourself in the future. Second, get portal, portal 2, and Half life 2. You're not a pc gamer until you've played those games lol. Far Cry 3 is always a good choice for a game. About the witcher. I really didn't like it very much. I thought the controls were too cointer intuitive, and I wanted its RPG elements to be better. Also, get Skyrim, and mod the Hell out of it. Bioshock is one of the best games ever made (get one, not 2 or infinite).