1. Red Dead Redemption II - Recently finished it myself and I never thought they could top the first one after it won someone like me over who was never into westerns, in such a big way that I even checked out the classic western Dollars Trilogy with Clint Eastwood. It's still one of my favorite games to date and while I recommend playing the first one as it provides context for key moments and informs much of what you'll be doing in the epilogue of the 2nd game, if you only had to play one, then it's easily Red Dead Redemption II.
It's Rockstar's magnum opus, plain and simple. I never thought another game could blow me away like Breath of the Wild did this soon, yet Red Dead Redemption II completely blows it out of the water with its beautifully detailed world that's both expansive and varied and its immersion that is unrivaled by just how alive the world and its NPCs are as well as its extremely deep mechanics and animations that further immerse you into the role of the character.
It's a true masterclass in storytelling and easily Rockstar's best story with possibly their greatest protagonist and cast of characters. Never thought I'd say that after the attachment I had to John Marston and his story from the first game, but it's well earned even long before the credits roll.
Games that stick with you the way these games have are rare, and Red Dead Redemption II is everything the first one was and way more. It's not even close and anyone who loves and appreciates video games as a legitimate form of art and storytelling owes it to themselves to play Red Dead Redemption II because it's truly an achievement in gaming.
2. Resident Evil 2 (2019) - The REmake of the original Resident Evil that ushered in the era of survival horror is still unmatched. It is a survival horror masterpiece that not only understands what made the original work, but also improved on just about every aspect of the game and set a new standard for the series itself which unfortunately chose to go in a different direction that would ultimately shape the series for the next 2 decades.
Horror games aren't for everyone, especially the classic kind, which are a lost art with their fixed camera perspective and trial and error nature that requires the player to get better at navigating and using/saving resources in order to progress more efficiently. That's why I'm recommending the 2019 remake of the iconic sequel, which comes the closest to the brilliance of the first REmake, but with modern gaming conventions that make it far more accessible to all gamers.
The truth about survival horror games, or the classic Resident Evil games in particular, is that they're not scary. They're metroidvanias by design and work just like a giant puzzle would. This is why each game grades you at the end, because you can become better at the puzzle. Skip a few steps, navigate better, and finish in record time.
I wish more people could look past the atmosphere and intimidating encounters and see the series this way and stop using being afraid as an excuse to not try these type of games. Yes, horror games aren't for everybody, but if they were to try just one and understand why people actually like traditional classic horror games from the past and not the cheap VR walking simulators they've been turned into today, then they can't go wrong with Resident Evil 2 REmake.
3. Tomb Raider (2013) - The 2013 reboot of Tomb Raider is massively underrated and often in the shadow of the very franchise it originally inspired. Most people like to cite Uncharted when they think of modern adventure games and I find that rather unfortunate. Uncharted is an action game about a man who goes on an adventure, not an actual adventure game. It's much too linear and focused on being a cinematic gaming experience, which is why it's such an excellent series, but the false comparisons between the two series and "rivalry" between its fans is very unwarranted.
Tomb Raider definitely borrows from the Uncharted series and to good effect, but it's got more in common with traditional action/adventure games that it's actually more of a modern metroidvania than it is an Uncharted "clone." It's no different from the Batman Arkham series, which I'd also strongly recommend, but Batman or superheroes in general might not be everyone's cup of tea, so you'd think Uncharted fans at the very least would be interested in giving a game like Tomb Raider with its similar ideas and mechanics a try.
Uncharted is by far the more popular franchise these days, but Tomb Raider is definitely the more rewarding experience with far more engaging mechanics, a character progression system, exploration, hunting, and puzzle solving, all with the explosive cinematic action of an Uncharted game. I can see how the more casual gamer might prefer the simplicity and straightforwardness of the Uncharted series, but any serious gamer would be robbing themselves by not playing Tomb Raider.
4. Streets of Rage 2 - Beat 'em ups have got to be the easiest games for anyone to pick up and play and were practically made for co-op. But what sets Streets of Rage 2 apart from most arcade beat 'em ups, whether it be Ninja Turtles, X-Men, The Simpsons, and whatever other popular IP from the 90s that were milked into arcade machines is that it's not an arcade game at all.
Being developed for the home console, the goal of Streets of Rage wasn't to steal your quarters with cheap enemy A.I. and a basic moveset that amounts to you just pressing the same 2 buttons repeatedly until you die. Streets of Rage 2 rewards strategy and skill and combat is actually tactile so you know when your hits are connecting, unlike in the arcade games.
Combat is also really reminiscent of fighting games like Street Fighter, with character movesets being greatly expanded by directional inputs but streamlined for a refined beat 'em up experience. Each of the four playable characters also have their own unique strengths and movesets, making your approach to certain combat situations vary from character to character.
The beat 'em up genre has been going through a bit of a resurgence as of late, and they're guaranteed fun with friends and there's no better game to start with than Streets of Rage 2 if you not only want to have fun, but also enjoy a legitimate gaming experience with a friend, which could open the door to many more experiences and maybe even be the perfect gateway to the fighting game genre.
5. Sonic Mania - I've been struggling to come up with a 5th game I can properly justify, but since it's already been brought up, I'd say I agree with Sonic Mania.
Sonic is a franchise that has long lost its way and is now remembered for all the wrong reasons that have left some people even questioning whether Sonic was ever really a legitimate rival to Mario as his games were never actually all they were cracked up to be.
As a longtime scrutinizer of the series, I'm inclined to agree that Sonic was never truly a rival to Mario's consistently high quality outings, but I strongly disagree with the notion that Sonic was never good as there's a reason why the blue hedgehog has been so persistent for all these years despite often missing the mark and even the point of what made Sonic the phenomenon that it was.
It took some time, but Sonic Mania finally reminded the world why Sonic the Hedgehog was special by going back to where it all started and applying all the lessons learned throughout the years to finally put Sonic's brilliant level design where speed is a reward and momentum is key front and center. Sonic may not be Mario's rival and truthfully, never was, but what he offered to the platforming genre cannot be understated and is still uniquely his own, and it doesn't get any better than with Sonic Mania.
Cyber Shadow-This game captures the essence of the NES Ninja Gaiden/Ninja Ryukenden games while improving upon it in countless ways, such as having great vertical level design in addition to horizontal, great physics, awesome bosses, etc. PLAY THIS GAME. It's so underrated. OST is great, too. 
