Not sure what my favorite would be, but I did recently play Code Name: STEAM (apparently known in Japan as "Lincoln vs. Aliens".....yeah), and I gotta say, that game doesn't get as much credit as it deserves. It is a pretty standard XCom-esque game, with some cool mechanics and a fun story. Some bits are overly frustrating and I think it could work together its story bits more cleanly, but I got it for about $4 and got 20 hours of fun out of it, so I have no complaints.
Off the top of my head, I found Just Cause 3 to be very fun, even if the framerate dipped to borderline unplayable levels.
Dead Rising 4 was pretty enjoyable for me as well. Huge step from that disappointment that was dead rising 3. I liked the fact that the stupid ass timer was removed, letting me play at my own pace. The more jolly, fun vibe fit the series way better than the last game. While yes, Capcom locking the ending behind DLC was one of the most anti-consumer things I've ever witnessed, I would still reccomend the definitive edition (frank's big package) to people who haven't played it yet. A very little known fact is that the game got a PS4 port too, late last year.
It's a shame that the game bombed, and Capcom Vancouver had to close down.
Bet with Intrinsic:
The Switch will outsell 3DS (based on VGchartz numbers), according to me, while Intrinsic thinks the opposite will hold true. One month avatar control for the loser's avatar.
Probably my favorite is Tak and the Power of Jujuone of the rare licensed games thats actually great. Its a gorgeous 3D platform-adventure game, in the same family as The Precursor Legacy, Psychonauts, etc.
Others are Red Dead Revolver, Epic Mickey, and Wolfenstein (2009).
The Evil Within just have 75 metacritic on PS4, is still in green, but it's my most underrated game by far. Its gameplay and visuals are not as polished as a Naughty Dog game, but game design, scenario, story, boss fights, set pieces are some of the best in this gen and is one of the best survival horror games ever.
But by your rules, by far the best sub 75 game this gen i've played and criminally underrated by its circunstances at launch is.....Assassin's Creed Unity (with 70 on PS4). Still one of the most gorgeus games this gen, with an ambition and detail recreating a historical setting we are not seeing anymore in the franchise. For me, it was the best old style AC alongside ACII. Its focus on stealth and how to realise how to kill your target is what i like about an Assassin's Creed game. Yes, it had bugs, yes it could be frustrating at times because you don't always do what you want to do, but RDR 2 have those same problems too and is a 97 rated game.
Pokemon Mystery Dungeon (either the Rescue Team games or the Explorers games, they're both around 50 on meta). They're the most underrated games in history imo. The reviews they got made me so fucking mad, the reviewers complained about the mystery dungeon genre, rather than the games themselves which are packed full of content, pretty, beautiful sounding and have the best stories of any Pokemon game (far better than any Pokemon game deserves to be.) They're easily my favourite games of all time and I'll take every chance I get to push them. I stopped paying attention to reviews or reviewers when buying games as a whole back then because obviously they have no fucking idea what they're talking about.
Tales of Xillia 2 - Builds on the vibrant world established in the first game, with a few new characters with very compelling stories, some amazing plot twists, and probably one of the coolest final boss songs I've heard in a JRPG.
If I had to justify its low scores, I'd guess it has to do with the game largely recycling content from the first game, but to me this is an example of a JRPG sequel done well. It's basically the type of sequel that I wish Symphonia got, instead of that cringey fanfic it got instead.
Bleach: The 3rd Phantom - I get games like this never seem to go over well with people outside the fanbase of the source material, but this game was well made enough that it deserved much higher than the ~60 score it got. Was a fun tactical RPG with a time management system, and gave cool opportunities to see characters interact outside of the canon, develop existing characters, and even learn your own zanpakutou and Bankai powers.
Star Fox Assault - Another game that didn't seem to go over well, but honestly my 2nd favorite Star Fox game to date. The arcade style combat was super fun, and I found myself replaying it over and over again until I got all the medals. Also had an amazing multiplayer mode, I remember my brother used to love trying random shit on Arwings, like jumping from ship to ship, or standing on each other's wings in pilot mode while we fought CPUs. Or crashing into buildings...though probably shouldn't brag about that part.