What types of games you know?

I start with

Dust : An Elysian Tail. A game you should really play!

Half-life & portal series

this is always my go-to suggestion: Planetship

Any game with an interesting story that will make me not care about everything else for the period that I'm playing it.

The Witcher: Enhanced Edition The Director's Cut. Many people skip on this one because of the clunky game mechanics and go straight for 2, but once you learn them you'll love the game. One of my favorite games ever.

Lisa and Masochisia

I really liked Alice Madness Returns and Life is Strange.
Currently playing Armello, almost always on online multiplayer, it's fun to play with friends

where are no platformers and fightings T_T

Stealth: Splinter Cell, Hitman
Open World RPG: Gothic 1-3 (we don't talk about Gothic 4, that does not exist)
Adventure: You mean point & click? Gabriel Knight Series, Broken Sword Series, The Feeble Files, Book of Unwritten Tales, and countless others.

un buon stealth sicuramente è l'ultimo thief. Open worlds: far cry 3, sleeping dogs.
Non perderti dishonored. Ciao!

I really liked Mark of the Ninja , it's a good stealth platformer !

Aragami, a little stralth game.
Also Shadwen.

Styx: Master of Shadows for the stealth genre :)

Stealth: Deus Ex series, old Thief games.
Open World: Morrowind, Oblivion (+ Nehrim, Enderal and other giant quest mods)
Adventure: Valiant Hearts, The Vanishing of Ethan Carter, Fran Bow
RPG: Neverwinte Nights 1+2, Baldur's Gate 1+2, Dragon Age Origins, Star Wars Knights of the Old Republic 1+2, Planetscape Torment, Vampire the Masquerade - Bloodlines
Action: Mass Effect 1+2+3
Puzzle: The Talos Principle, Portal 1+2
Rnadom: The Stanley Parable, Papers Please, Scribblenauts

Ti consiglio Deus Ex: Human Revolution (trailer).
DE:HR è un gioco d'azione con elementi di gioco di ruolo. Puoi sviluppare il personaggio potenziando cose come la forza fisica, la protezione, la mobilità, la furtività, la capacità di violare i terminali, la mira. Puoi eliminare i nemici, stordirli o semplicemente passare inosservato. Puoi accedere a pc o altri terminali (come tastiere numeriche che gestiscono porte, sensori o allarmi) violandoli, cercando in giro i codici di accesso oppure usando dei dispositivi automatici usa e getta. Quando non sei in missione, puoi parlare con le persone e farti dare informazioni o missioni secondarie, esplorare la zona e scoprire segreti.
Secondo me è un ottimo gioco, l'ambientazione è molto ben riuscita grazie anche alla colonna sonora, la storia è avvincente ed è molto lunga se si fanno anche le missioni secondarie (ci ho messo circa 35-40 ore la prima volta), mi sono divertito molto a completare tutte le sfide.
Lo puoi trovare a 4-5€ quando è in offerta su Steam, oppure anche a meno su altri siti.

RPG: The Legend of Heroes: Trails in the Sky & The Legend of Heroes: Trails in the Sky SC, I only played the first one, but probably the second is even better. (BTW, you have to play them in order).

Plataformer -> trine 1 + trine 2 + some old tomb raiders (1,2,3,4)
Strategy -> dawn of war 2 (the game + 2 expansions) + company of heroes 2 + age of empires 2 and 3 + skull of the shogun
Action -> strider + Ys origin + tomb raider 2013
Racing -> trackmania canyon
sports -> rocket league

specials mentions -> bioshock infinite / hyperdimension neptunia 1 and 3 / Fallen Enchantress: Legendary Heroes (whit all DLC) / Lara croft and the guardian of light / lara croft and the temple of osiris / the last remnant / Shogun 2 total war (whit all DLC) / Praetorians / Shantae and the Pirate's Curse / The walking dead (both seassons) / 100% orange juice and a long etc.....

but there's a lot of nice games and also a lot of overrrated games too that people keep making recomendations when they are just shit. (example: portal games, easy puzzles and the only history it's the joke of the cake that keep going during all the game)

and obviously there's a lot of underrrated games too that are magnific games. (example:blackguards 1)

I'm a massive stealth fan, to the point of it being a bit too unhealthy for me :D Here are my suggestions:

Stealth: Hitman, Splinter Cell, Styx Master of Shadows, Volume, Gunpoint, Aragami, Deus Ex, Shadwen, Death to Spies, Commandos, Mark of the Ninja. There are some other titles in this genre I have in my library but I haven't played them yet. For example Invisible Inc is said to be among the hardest stealth games available. I'm curious to play games like Neon Struct, Dark, Marvelous Miss Take, Solarix, Calvino Noir from my library but my backlog priorities lie elsewhere at the moment. If you find Hitman too expensive, you can try its indie alternative Alekhine's Gun.

As for open world you can't go wrong with The Witcher 3. Best RPG ever in my opinion.

I don't play much action games but if you find a co-op friend, definitely go for Borderlands games. Borderlands 1 is too tedious and grindy for me but I particularly loved Borderlands The Pre-Sequel and then Borderlands 2.

Adventure will be a bit tricky because there are so many variations of them, what type of adventure are you talking about? Is it point and click type of adventure like Life is Strange, Deponia etc or a bit action oriented like Tomb Raider? Nevertheless, my favourite ones are Machinarium and Tales from the Borderlands. I'd suggest any Telltale game for adventure category with the exception of Jurassic Park the Game. Monkey Island and Sam & Max are quite funny adventure games as well.

Edit: I just saw your reply to another user regarding Adventure games. So scratch my recommendations as they are point and click. I'll suggest Tomb Raider and Rise of the Tomb Raider. I generally prefer point and click adventure so I don't know any more titles regarding that particular "go explore" type of adventure you are looking for other than Tomb Raider series.

little bit from most of the categories.

not a fan of top-down (over head world down view) in any category at all.
not a fan of some artwork style games but others i do like (don't care for borderlands cartoon-like vibe, but love long darks abstract-like vibe)...

otherwise i can be a little picky still on other games, but love the majority of the rest.

rather surprised to see FPS that low in poll rankings, but then again RPG i'm not surprised at all is that highly ranked.

Personally i enjoy RPGs the most both in video game and table top form, and one such lovechild of the two that i will always have a fondness for is the original Baldur's Gate as a kid if blew my mind "Video game D&D?! hell yeah!!!" cept y'know, i was a kid, so it was more of "heck yeah"

for action games I'd suggest shank, enter the gungeon, darksiders 2 and Devil May Cry 4 Special Edition
for stealth mark of the ninja is really amazing, there's also monaco and metal gear solid 5 the phantom pain.
For open world, sleeping dogs is really good and often overlooked.

Unaware?
Well…

Remember Me is slowly getting out of the abyss and people recognise it as a great narrative-oriented action game.

In the sea of generic console shooters with their sissy health regen and cover system, Serious Sams still stand out as shining beacons of real first-person shooters. Doom 4 as well, but that is hardly obscure. (But more hardly kicking ass.) Or, if you want to play a kiddie shooter, at least play Star Wars: Republic Commando. On highest difficulty, it has actual challenge and requires planning.

I can never tell enough people how great a hidden object game Brink of Consciousness is.

Beyond Good & Evil still not enjoying appropriate status for being a game defying genres.

Still Life is one of the best point 'n' clicks ever made. it oozes atmosphere all around. Syberia 1-2 is close, but there the arcing story is the great addition, as the games are sloooooooooooooooooooooooooooow as hell.
Also, many, many games published by Wadjet Eye are great indie point 'n' clicks (on an incredibly terrible engine).
And still speaking of point 'n' clicks, the Book of Unwritten Tales series. It is slightly crumbling under its own ambition and PnC following status, but it still holds and didn't derail yet.

Belladonna is actually a pretty damn good casual linear adventure game. Especially if you like the strange and eerie, but not the necessarily cheaply scary kind.

Stacking is a rather forgotten entry in the Double Fine portfolio, even though it is a very fun little puzzle/adventure game that is among the few of its kind that doesn't want to be a platformer for no apparent reason (coughPsychonautscough).

Septerra Core is one of the most unjustly forgotten Western JRPGs of all time. And essentially the only Western JRPG I know of that wasn't made in RPGmaker.

Hexoscope is a recent puzzle game, goes for one buck on Steam, and it is gloriously brilliant.
Speaking of puzzles, Neighbours from Hell 1-2. If you are from Central/Eastern Europe, your head may have started to nod in approval instinctively.

If you like cRPGs, the Trokia games are worth a look. And a lot of patience to patch them to working status. Arcanum is one of the most complexly woven cRPG ever (the first act has more plot threads than all Elder Scrolls put together and multiplied by the amount of dollars Bethesda earned for them), even if it suffers from an exploitable combat system.

People are all about the XCOM remakes, but it just shows how few of them played the original games. Get OpenXcom, try to survive the first month, and you'll laugh at the "difficulty" of that console game they made it into. (You may also try Xenonauts as it is a more faithful XCom remake, but it still has issues.)

RTS has many hidden gems. Total Annihilation is luckily not forgotten, but one of the best RTS games ever made, Ground Control, is. And if you thought Company of Heroes was complex, try Commandos 1 and expansion or to juggle three real-time combat zones in Metal Fatigue (which seriously has to be on GOG, like right now).
If you want the more peaceful strategies, the last entry of the 2D Sierra City Building series, Emperor: Rise of the Middle Kingdom is an unjustly forgotten best entry in a good series.