Here is a command you can simply paste into your terminal to install most of the best available Ubuntu games, emulators, and media players that do not require external repositories and that are available on the 64-bit ‘amd64’ architecture. You do want to make sure you have the universe and multiverse enabled.
$ sudo apt-get install neverball tremulous nexuiz neverputt flightgear wesnoth openarena glest sauerbraten frozen-bubble planetpenguin-racer supertuxkart pingus extremetuxracer warsow scorched3d beneath-a-steel-sky flight-of-the-amazon-queen fretsonfire torcs armagetron bzflag einstein blobwars supertux sopwith airstrike chromium lincity wormux xmoto nethack-qt angband criticalmass enigma uqm kmahjongg xpilot-ng rplay-client rplay-server lbreakout2 oolite vegastrike freeciv-client-sdl warzone2100 fillets-ng alienblaster gl-117 mu-cade simutrans xqf monster-masher egoboo sauerbraten singularity slune smc snowballz solarwolf supertux supertuxkart scorched3d titanion tmw toppler trackballs tumiki-fighters tuxpaint tuxtype tuxmath torus-trooper val-and-rick warsow vegastrike wesnoth whichwayisup widelands wormux wound-up xmoto lordsawar lincity-ng lightyears mazeofgalious monkey-bubble mu-cade noiz2sa oolite orbital-eunuchs-sniper parsec47 pinball pixbros pixfrogger plee-the-bear powermanga pydance rrootage pyracerz frotz jzip qtads xzip renpy renpy-thequestion renpy-demo kanagram kbattleship khangman kollision hedgewars hannah gunroar gtkboard fretsonfire enemylines3 enemylines7 glob2 gltron gnujump gnome-games gtkboard glest funnyboat gamine freedroid freedroidrpg freeciv-client-sdl freeciv-client-gtk childsplay csmash conquest fillets-ng epiphany cheese cheesetracker btanks boswars a7xpg abe adonthell adanaxisgpl angrydd balazar balazarbrothers balder2d blockattack csmash csmash-demosong freeciv-sound vorbis-tools mp32ogg tuxpaint-config gqcam qcam childsplay-alphabet-sounds-de
$ sudo apt-get install gfceu efp wine dosemu dosbox atari800 vice mednafen desmume zsnes gngb pearpc pcsx-bin openmsx qemu kqemu-source visualboyadvance visualboyadvance-gtk basilisk2 dgen gnuboy-sdl yabause-gtk snes9x-x sdlmame spectemu-x11 uae stella xtrs xmess-sdl psemu-sound-alsa psemu-input-padjoy psemu-drive psemu-video openmsx-catapult sdlmame sdlmame-tools joystick
$ sudo apt-get install gecko-mediaplayer mplayer w64codecs libdvdcss2 xpdf flashplugin-nonfree timidity pmidi sun-java6-jre sun-java6-jdk bristol
$ sudo apt-get install mingw32 fakeroot screen opera