Oh boy, I have quite a few of these but the big one for me...
DARK SOULS II
I will die on this hill, Dark Souls II is NOT a bad game, it's actually extremely high quality with a ton of content and creativity, highly varied obstacles and environments, an absurd amount of unique items and spells to play with, and overwhelmingly the best PvP in the series. The problem is it has some pretty glaring, objective flaws that stick out a LOT more because it's being stacked against DeS and DS1, two games that are very highly regarded and set certain expectation. DS2 outright fails at a lot of those games' best assets, but makes up for it in spades in other ways. It also introduced tons of new mechanics that were (mostly) excellent additions; powerstancing, bonfire ascetics, level respeccing, lowering spell requirements, a proper torch system, pharros lockstones (and the associated covenants), twinblades, not getting kicked from the game for a DC, greatly improved equipment upgrades, actually meaningful changes in NG+, breakable chests and doors, etc.
That last one, in particular, does not get enough love... the environmental interactivity in general is crazy, like the door in Forest of Fallen Giants that will NOT open normally and isn't locked; instead, you 'knock' on it by hitting it, and the enemy inside opens it. Or the wooden door in the same area that can be opened by a key you get later... or you can break it down early. The pools of oil in the Gutter and Black Gulch that hide enemies inside them, but if you light them on fire the enemy slowly dies, or the Gutter's ingenious level design encouraging systematic torch use and sconce lighting, even rewarding you with an event if you light all of them. I'd even mention the windmill. Sure, it wasn't super well implemented, but the actual use of the environment, an optional action you can take to literally change the entire area and reduce its difficulty by removing the poison water? Well done or not, it's very creative.
Also, the little touches... the weird stuff, like the Shulva tree that repairs your equipment instantly, but only if you whip it. They even include a notched whip in the room as a hint. How about the crypt? There's a semi-major NPC who tells you immediately not to produce light, even though the area is really dark; he remains friendly and even helpful if you listen to him, and even his body guards remain passive.... but if you light a torch? They're all coming for you. I particularly love the first merchant and how his quest works, where he's this humble and crestfallen merchant who offers a small selection, but the more you spend the bigger his stock is... and the more pompous he is as a result. Despite this, though? The 'happier' and more successful he is, the more he loses himself, the further he gets from who he really was and what he wanted... and the further his humanity dies. Then, of course, Lucatiel; she's a masterfully done NPC that really deserves a lot more love.
DS2 is simply a fantastic game that has so much to offer, but as a SOULS game? It's... really actually quite different, especially on the expectations side when compared to the previous entries. It feels less horror and more adventurous. Less sorrowful and more hopeful. The areas are far more 'video gamey' and linear, while the world is a lot less concerned with being intricately interwoven and immersive. This game wants to be fun and full of lots to find and lots to do, it wants you to go on adventures and find treasure and take down fierce enemies to feel glorious.
Some others I'd like to mention more briefly...
DmC: Devil may Cry AND Devil May Cry 2: They're both really fun and have a lot of great stuff in them. DmC in particular has some amazing gameplay and some really fun weapons, it's just... very different and at times incredibly cringey. DMC2 is a lot 'closer' but just different enough to feel off, they drastically alter Dante into a far more series and brooding character, and it can be pretty 'grindy.' There's so many unique fights and moments, though, and both characters not only playing very differently but having very different playthroughs (even different final bosses) was awesome.
Twisted Metal 4: This game is such a blast to play with so much charm and just feels... fun. It's very playful and colorful, exploding with personality and fast, frantic gameplay. Some of the best maps in the series come from this game, and there's very few maps that aren't at least good, and there's just a lot of content. It's VERY different from the earlier entries, and sometimes borders on character assassination, but it's just so enjoyable. Also, a particularly killer soundtrack.
Super Mario Bros. 2: Considering it is LITERALLY not a Mario game originally it's going to be very, very different... but it's just a really, really good game with a lot of charm. That said, it did add a lot to the Mario universe going forward and gave us some of the greatest enemies in the franchise (Shy Guys, anyone? Ninjies?) Also, it's just a LOT more varied in its gameplay than the first SMB. I love the first SMB, but I think between SMB3 giving us the same thing as the first but WAAAY more and perfected, and SMB2 offering something entirely different, there's a lot of reason to give this one a fair shot.