This article features the 12 best games (in my opinion) in term of quality and fun available in OpenBSD packages. The list only contains open source games that you can install out of the box. This means that game engines requiring proprietary (or paid) game assets are not part of this list.
Tales of Maj'Eyal
Tome4 is a rogue-like game with many classes, many races, lot of areas to explore. There are fun pieces of lore to find and read if it's your thing, you have to play it many times to unlock everything. Note that while the game is open source, there are paid extensions requiring an online account on the official website, this is not mandatory to play or finish the game.
# pkg_add tome4 $ tome4
This famous game is a free reimplementation of the Transport Tycoon game. Build roads, rails, make huge trains networks with signals, transports materials from extraction to industries and then deliver goods to cities to make them grow. There is a huge community and many mods, and the game can be played in multiplayer. Also available on Android.
# pkg_add openttd $ openttd
The Battle for Wesnoth
Wesnoth is a turn based strategy game based on hexagons. There are many races with their own units. The game features a full set of campaign for playing solo but also include multiplayer. Also available on Android.
# pkg_add wesnoth $ wesnoth
This game is about space exploration, you are captain of a ship and you can get missions, enhance your ship, trade goods over the galaxy or fight enemies. There is a learning curve to enjoy it because it's quite hard to understand at first.
# pkg_add endless-sky $ endless-sky
Open Red Alert, the 100% free reimplementation of the engine AND assets of Red Alert, Command and Conquer and Dune. You can play all these games from OpenRA, including multiplayer. Note that there are no campaign, you can play skirmish alone with bots or in multiplayer. Campaigns (and cinematics) could be played using the original games files (from OpenRA launcher), as the games have been published as freeware a few years ago, one can find them for free and legally.
# pkg_add openra $ openra wait for instructions to download the assets of the game you want to play
Cataclysm: Dark Days Ahead
Cataclysm DDA is a game in which you awake in a zombie apocalypse and you have to survive. The game is extremely complete and allow many actions/combinations like driving vehicles, disassemble electronics to build your own devices and many things I didn't try yet. The game is turn based and 2D from top, I highly recommend reading the manual and how-to because the game is hard. You can also create your character when you start a game, which will totally change the game experience because of your characters attributes and knowledge.
# pkg_add cataclysm-dda $ cataclysm-dda
Taisei is a bullet hell game in the Touhou universe. Very well done, extremely fun, multiple characters to play with an alternative mechanic of each character.
# pkg_add taisei $ taisei
The Legend of Zelda: Return of the Hylian SE
There is a game engine named Solarus dedicated to write Zelda like games, and Zelda RotH is a game based on this. Nothing special to say, it's a 2D Zelda game, very well done with a new adventure.
# pkg_add zelda_roth_se $ zelda_roth_se
This game is about making industries from shapes and colors in order to deliver what you are asked to produce in the most efficient manner, this game is addictive and easy to understand thanks to the tutorial when you start the game.
# pkg_add shapezio $ /usr/local/bin/electron /usr/local/share/shapez.io/index.html
OpenArena is a Quake 3 reimplementation, including assets. It's like Quake 3 but it's not Quake 3 :)
# pkg_add openarena $ openarena
This is a fast paced arena FPS game with beautiful graphics, many weapons with two modes of fire and many games modes. Reminds me a lot Unreal Tournament 2003.
# pkg_add xonotic $ xonotic
This game is a rogue like (every run is different than last one) in which you move from hexagone to hexagone to get points, each biome has its own characteristics, like a sand biome in which you have to gather spice and you must escape sand worms :-) . The game is easy to play, turn by turn and has unusual graphics because of the non-euclidian nature of its world. I recommend reading the game manual because the first time I played it I really disliked it by missing most of the game mechanics... Also available on Android!
And many others
Here is a list of games I didn't include but at also worth being played: 0ad, Xmoto, Freedoom, The Dark Mod, Freedink, crack-attack, witchblast, flare, vegastrike and many others.