Hello Cfriedma.
I'm really sorry to here about your husband. I'm afraid making game recommendations might be slightly difficult, sinse I personally have litle knolidge or expertees when it comes to other difficulties with gaming like Motor or mobility issues.
I would however advise you to ask on the forum at Game accessibility.com, a site dedicated to various accessibility related issues in gaming, with people who can hopefully give more general advice about issues such as keyboard accessibility in games. I believe there are various pieces of hardware available which can map certain keyboard functions onto more easily useable buttons or the mouse. Sinse many audio games, ----- including Dark destroyer which shin Goenitz mentioned above, use only a few keyboard keys, these kinds of things might be helpful.
You mention that your husband is able to use a joystick. While many audio games can be played via a joystick, most require use of multiple buttons on the joystick as well as moving the stick itself. In a space invaders game for example, you'd move your player with the joystick and use other buttons to shoot, activate different weapons, speak various in game info etc. If this is alright,then there are quite a few audio games which would be playable. In the space-invaders genre, there's troopanum 2 by Bsc games or Alien outback by Draconis Entertainment, to name but a few. I'd highly recommend the most recently developed space-invaders game, Judgement day by L-works, not only does it feature extensive unlockable game content and quite a range of difficulty modes, but it is also playable using a mouse which might be a possible alternative if your husband doesn't find using joysticks with multiple buttons a reasonable option.
finally, the free game Access invaders offers a range of different controle schemes and customizations which might be useful.
As to 3d Fps games, there are several available, but most require fairly extensive use of a joystick's buttons. If this is okay, you might considder investigating Shades of doom from Gma games, an audio game in the style of original Doom which also features symple black on white graphics. Then there is the audio quake project, an attempt to make the quake game engine accessible through audio. What the controls in audio Quake are like I'm afraid I don't know, sinse I haven't got around to trying the game, but you can find out more on the Agrip site
though most audio games do not feature graphics, Terraformers from Pin interactive features the normal graphics of a 3D fps game, but is entirely playable just using the audio. Sinse this is also a game I haven't investigated fully though, I'm again uncertain as to how the controls work.
Speaking of controls, there is only one audio one switch game I know, Tampokme, the audio multiplayer one switch mosquito eater, a free and symple game in which you control a carnivorous plant. you can Directly download the game here
apart from Terraformers mentioned above, not many audio games feature graphics I'm afraid. Shades of doom, and Packman talks (an audio adaptation of the classic arcade game), feature high contrast white on black block graphics, as does Sarah and the castle of Witchcraft and Wizardry, a 3D puzle and adventure game produced by Pcs games (if your husband is a Harry potter fan and okay with multiple button joysticks, I can absolutely recommend this one).
then, there's the Sonic Zoom game, a free and symple racing game developed by Sounds like fun, which again features graphics, but is playable just using audio.
Various games produced by The american printing house for the blind also apparently feature high contrast graphics, though as i seem to have trouble running these games, I can't say what the control or gameplay is like.
You mention that your husband is "Legally blind" if he stil has some useable vision, I can highly recommend the free game Archaist. this is a remake of the C64 game Pase maker. It's a scrolling shooter with strategical and item collecting elements, which may be played with 1 or 2 players. though it isn't an audio game, it does feature a host of options to customize the game in various ways. These include the option of extremely high contrast graphics with several colour sets, the use of Microsoft Sapi to speak all in game menues and text, many alternative control schemes including 1 key and mouse only, and the ability to easily customize just about all aspects of gameplay, such as game speed, the frequency, number and type of enemies, amount of extra lives and more!
If you'd like to know more about Archaist, your welcome to mail me off list (I was a beta tester for the game), my address is dark at x g a m dot org.
I hope some of these links and other information has been useful to you.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)