NM food is different than Mexican food in TX or Tex Mex. Keep that in mind as you try it in NM. I would say the biggest shock to most Tex-mex fans is less extreme seasoning, salt, and cumin and more fresh chile flavor.
The Shed/La Choza/ Maria'sThe Shed is popular. People like it, and its cool to hate on it, but empty restaurants don't last, and this one is an institution, If you like to go to well-traveled places with a lot of traffic and history, embrace the tourist and local popularity and check it out. If you don't like crowded spots, there are plenty of options that aren't as packed. These three restaurants all serve phenomenal red chile enchiladas and great margaritas in Santa Fe, which is what I think of as the classic Northern New Mexican dinner.
The Shed and La Choza are owned by the same family, and they have the great red chile .Get the Enchilada Plate, Red, with extra onions, and a silver coin margarita (optionally with a float of mezcal). They will ask you if you want sopaipilla or garlic bread, and the answer should be, "Is there any way I can get both?" The Shed is the more storied and popular touristy location of these. There will be a long wait - sometimes if you call in advance you can get a reservation, but usually even then they give you a buzzer and you have to wait. Find a way to enjoy it if you like popular places. I have some other off-the-beaten path joints in this list too, but
Maria's is the main competition for The Shed, with similar culinary strengths - their red chile is good, but not quite as good to me as the former but their margaritas are better. In short, these are the 3 heavy hitters in Santa Fe with lots of traffic and history.
https://www.lachozasf.com/https://www.marias-santafe.com/Horseman's HavenDespite appearances, Horseman's Haven is a temple to green chile. Its attached to a gas station out on Cerillos, with photos of a few local sports teams and locals eating breakfast at beat up linoleum tables. They don't have a website, I'll just include the address, but if you Google it it's readily found. Their green chile is the best in the world. Warning - it is also legitimately hot. The best thing to order here is a breakfast burrito with green chile, but the 3D burrito with green chile is also excellent (adovada is a strong play), and their green chile cheeseburgers are amazing The pros all stick to bacon in their breakfast burritos, but personally I like to go with chorizo; everyone agrees, though, that you want to ask for the potatoes extra crispy and get your burrito smothered in green chile and cheese. I like to get a side of level 2, but you don't strictly need it unless there is something wrong with you - the normal level 1 green chile will already light you up good. Don't make plans to operate heavy machinery after eating here.
4354 Cerrillos Rd, Santa Fe, NM 87507
Tia Sophia'sThey close early. Great green, but their red is also killer. Can't go wrong with the Atrisco plate, but I think everything there is pretty great. If I'm extra hungry and can convince someone to split it with me, I like to get a single blue corn pancake on the side and cover it with a side of green chile, which I know sounds crazy but trust me it's awesome.
210 W San Francisco St, Santa Fe, NM 87501
El ParasolLocal chain. Their shredded beef tacos and their chicken tacos with guacamole are some of the very best tacos I've ever eaten, get some of their hot sauce too. The burritos are killer too, I like their bean and cheese. This is a no-fuss, simple taco-stand type place with foil wrapped tacos or foam takeout container plates. All of which are great.
https://elparasol.com/
Rancho de Chimayo (outside of Santa Fe, but a reasonable day trip, or you can stay there - see below)
This place is a true temple to red chile, and, unlike Horseman's, it lets you know it's a temple. Behind the beautiful terraced seating out back there is an old wooden gate you can walk through to a quiet rolling kind of dried orchard, which seems utterly magical. While in Chimayo, admire the Spanish colonial art in the nave of the sanctuario, get yourself some holy dirt, and stop by El Potrero Trading Post to buy the highest quality dried red chile I know how to find with any regularity. It can also be fun to buy chile from people selling it in the parking lot, though obviously that's more of a crap shoot.
https://www.ranchodechimayo.com/https://www.nps.gov/places/el-santuario-de-chimayo.htmhttps://santafelibrary.org/wp-content/uploads/sites/18/2022/05/Chimayo.pdfEl Modelo- If you are going to ABQ(outside of Santa Fe, down in ABQ)
There are other storied eateries down there, but in my admittedly limited experience none of them hold a candle to this place. Big plates/portions, in and out quick service take out only I have not really explored the menu here, because I don't go often, and every time I do I feel compelled to get either their chile relleno burrito or stuffed sopapilla. Which is a shame, because I suspect their Carne Adovada Burrito might actually be the best thing to get. Anyway, this place is amazing. No seating, but there are a precious few picnic tables in their parking lot.
https://www.elmodelomexicanfood.com/Honorable Mentions:
The Pantry- I'm surprised i didn't see this one reccomended. Incredibly solid Santa Fe mainstay, great diner food and great New Mexican food, excellent red and green. I once figured out the perfect order here, but I can never remember it - maybe it was a carne adovada omelette? That sure sounds perfect as I type this... friend always gets the Buenos Dias plate, usually Christmas. Man, I love this place.
https://www.pantrysantafe.com/Santa Fe Bite- Get the burgers here. At one point, it used to be the home of the best burger in the world. Now the home of a damn fine green chile cheeseburger, probably still the best in the city (though Horseman's might have something to say about that) and still one of the better burgers in the world.
https://www.santafebitenm.com/homePosa's- The best NM style tamales in town, fueled by red and green (you want the red). Their burritos are also serious contenders for best in town.
https://santafetamales.com/Cafe Pasqual's - takes a chef-y, high-end approach to New Mexican food, serves a killer breakfast but there will be a wait. And a pricetag.
https://pasquals.com/Clafouti's - in case you need a break from New Mexican food, this French cafe is really great. Absolutely killer pastries, too.
https://www.clafoutis.biz/Harry's Roadhouse- cool, a favorite among the locals, run by good people, serving reliably good food.
https://www.harrysroadhousesf.com/La Reina- Cool/hip tequila/mezcal/margarita bar in El Rey Court. a fixed-up old Route 66 motel.
https://elreycourt.com/la-reinaThe Matador - if you need a dive bar in Santa Fe, this is it.
116 W San Francisco St, Santa Fe, NM 87501
I figured I might as well go all the way. Hope this is useful, or at least decent reading. If you go to any of these spots let me know! I also have places to visit and stay/lodging recs if you need more rec's!