1) Above all else, I love how it plays like an updated MK2. The impacts are perfect, it feels hard and heavy, there's time to stop and think, it's not ridiculously fast like MK3, it's not 'floaty' like MK9 and MKX (I love those games but something always feels off with their jumping attacks, like there's not enough gravity), it just feels fantastic; very oldschool yet modern simultaneously. So many moves play like they used to, Kung Lao's dropkick, Mileena's teleport kick, my brain is wired to a lot of those old school inputs so to have them still be the same just feels so natural to a crusty old fan like me. Think this one covers a lot, so there's probably stacks in my number 1 here that could be covered by different entries. But I'm filing them all under 'classic gameplay'.
2) Needless to say, it looks amazing. They all like like actual people (or monster people in some necessary instances, but intentionally so at last), none of the weird wet clay skin and distorted faces of MKX, none of the dated oversized Shenmue hair from MK9, the bar has been set so high for MK12 I can't imagine how good that will look.
3) Customisation. Oh my god. I love this sooooo much. Yes I think it's undercooked (some characters like D'Vorah and Jacqui have terrible gear choices, there's not enough celebratory gear from other entries of the MK multimedia universe when this was an opportunity to give people practically every mask from the old games to the films and TV shows, whilst too many skins are revolting colour choices etc.) and the grind can be fiendish, but to have my characters look the way I want them to? I utterly utterly love that. Please be a staple of all MK moving forward, I never ever want this taken away. I love seeing other players' creations when I play in KL, I've spent hours upon hours designing my characters with different wardrobes, different names, different logos, hell I'm still doing so right to this day, for me it's like a whole game in itself. I love knowing that my Kitanas probably look nothing like yours and that I can even choose my own announcer (it's a crime there's no Shang, but Jennifer Hale's Kronika is the best since MK2/3's Shao Kahn IMO). I have "my" MK11, you have "your" MK11, and I love that so much.
4) I'm delighted the world and atmosphere has taken a step back from the death metal apocalypse of MKX to a more mystical and Asian influence again, didn't like that game's world much at all. It's not to MK1 or MK9's beautiful extent, but it's a big step forwards from the last game. Shirai Ryu Fire Garden, Shang Tsung's Island Ruins, Wu Shi Dragon Grotto and Shaolin Trap Dungeon are all such wonderful stages.
5) Story mode and single player content. Who'd have thought it would be possible to give the single player mode so much content to play and explore. From a fantastic story that was later expanded, with two possible endings, an interactive explorable version of Shang Tsung's island from MK1 and MK9 narrated by Cary Hiroyuki Tagawa in the Krypt, to the practice mode, towers of time, the gauntlet, the character towers; there's weeks upon weeks of things to progress through as a single player in a game that was born from being a two player coin-eating arcade game.
Love MK11, my criticisms are all aesthetic things that I just feel were wasted opportunities BECAUSE I love it so much. Shang announcer, movie gear from MK95 and MK21 (they don't need skin and voice packs if that's too much work and money, just give us masks and costumes for the ninjas etc. - fans would gladly do it for free if they had access to the modding tools), cloth masks for all the ninjas like Shang and Rain's fatality have access to, expansions to the Krypt, having revenant skins talking like revenants, not being able to put Kitana's Kahn mask down; it's all shallow pointless stuff that I'm sure many are reading thinking I'm insane regarding those things when they have their own personal issues with the gameplay. However I love the game exactly as it plays, I just wish they could have knocked it completely out of the park on all the new features I love, rather than just to the edge of the field.