Need some recomendations

Start with the rest of the Fallout RPG's.

do you like diablo esque?
try Grim Dawn or Titan Quest

If you liked the first Fallout, you'll probably enjoy Wasteland 2.

Knights of the Old Republic isn't exactly a hidden gem. But it is worth playing very much.

Grotesque Tactics series (Including the Holy Avatar game) are a very silly variant.

Lords of Xulima seems to be the most recent hidden gem, in that I don't recall seeing much marketing for it, but it's supposed to be really good.

Being a bit obvious:
Planescape Torment
Baldur's Gate (whole series)

Some of the newer stuff:
Pillars of Eternity seem to be good (hven't checked them out yet)
Shadowrun Returns (althought, pretty linear compared to the rest in the list)

Arcanum: Of Steamworks and Magic Obscura. Same developer team and similar gameplay, even more complex world and a plethora of routes to take in almost every quest and task. Combat is unbalanced though (depending on your chosen weapon class you either faceroll or die every time).
Lionheart, if you are a really patient type…
Stick of Truth, if you like South Park.
Deus Ex 1 and maybe 3 (Human Revolution).
Vampire, the Masquerade: Bloodlines, if you are patient with setting up stuff.
Most BioWare games starting from Baldur's Gate 1.

Since you put Fallout 1 up there, I'm guessing you don't mind the really old stuff. :p

Daggerfall is a DOS-game ancestor to the better known Skyrim. Going in the same tradition, it has a lot of exploration to do (and bugs to contend with), but I've always found it a little gem of a game. It's been released as a free download. It needs DosBox to run on most machines, but the setup is easy enough.

Arena is even older; the predecessor to Daggerfall. It's where the Elder Scrolls started. I feel Daggerfall is a straight upgrade to Arena, but you never know. ;)

Check the UESP if you want to scope the games a bit, first.