By rights, Hacienda should be a great leap forward for Mexican food in Melbourne. Chef Ross McCombe spent seven years working in Mexico City – including at highly regarded Quintonil – and still operates a couple of businesses there. At Hacienda, on the first floor of the Southgate development facing the river across from Flinders Street station, he’s not looking to give us the street food that dominates the Mexican food scene here (and elsewhere), but rather to show us what modern Mexican can look like.

Mexico City is one of the most exciting places in the world to eat, thanks to its endless markets, food stalls and cafes, but also because modern Mexican and Latino fine dining is better than ever. The cocktail scene there is on fire. Three Mexico City venues are on the World’s 50bestrestaurants list (including Quintonil, at no. 7) – a tally surpassed only by Bangkok, which has four.

In Melbourne, the past few years have brought a boom in quality tacos and even a few places doing regional specialties. With the opening of Barra and Morena, Alejandro Saravia is looking to showcase South American flavours in upscale and more casual settings alike. But Hacienda is pointed in its ambitions. On the Southgate website, it warns that this is “NOT your average street food offering”. McCombe is going so far as to make his own tortillas: an arduous process that pays off – the warm, corn-rich rounds you get with many dishes are fantastic – dusky and pliant in all the right ways.

In fact, much of the food here is fantastic. And while Hacienda aims to remove itself from the taco crowd, one of its best deals is the daily lunch, in which you get three tacos and a drink (beer, wine or agua fresca, the fruit- or flower-flavoured water like cordial but less sweet and more refreshing) for $25. The afternoon I visited, the daily taco was a juicy and generous serving of lamb birria, slow-cooked and wrapped in those tortillas with a side of lamb consomme for dipping.

On the Cold Bar section of the menu, there’s a Pacific Coast ceviche ($28) that is refreshing, bracing and addictive. A mix of prawns, octopus and fish in a lime-heavy marinade, it is served with crisp tortillas.

McCombe serves two huge marrow bones ($25) cooked in adobo and topped with a flurry of coriander, along with warm tortillas for wrapping. The marrow is rich and wobbly and perfectly rendered.

But there are oddities, inconsistencies and straight-up missteps that sap potential. Most are small: that bone marrow comes without an appropriate utensil for scooping its contents into your tortilla, turning a highly pleasurable experience into something frustrating. Oysters topped with a mole mignonette ($32 for six) would have been glorious if the oysters had been colder, or even slightly chilled. Speaking of temperature, a glass of Monte Tondo soave ($16), one of the more food-friendly white pours on this wine list, came warmer than room temp.

Why are share dishes, most commonly split between two people, served with three tortillas? Every time I was delighted by something at Hacienda, the next thing made me scratch my head.

There are some head-scratchers on the menu, too. A crab tostada ($28) was slightly sloppy rather than firm and fresh, and came with what was advertised as a coconut and brown butter emulsion but tasted like a weird cheese foam, overwhelming the delicate crab.

One of McCombe’s greatest achievements here, a deep brown, beautifully spiced peanut mole, is served with a massive hunk of pork belly ($52) fatty enough to vanquish all but the most devoted lard lovers. I ended up leaving most of the lechon and sopping up the sauce with my 1.5 tortillas, wishing for another less aggressively blubbery conduit.

Why are the origins of the margarita described below a cocktail that is not a margarita? There aren’t any margaritas served here – a bold choice – but the Tepache Sour ($25), made with mezcal and tepache (a pre-Colombian fermented pineapple drink), is a good substitute. Overall, cocktails are hit and miss with just as many veering into overwrought weirdness as those that make sense.

This is a restaurant of dichotomies. Some of this food left me giddy. But the room feels like a corporate chain, river views and all. Service is weirdly uneven despite the enthusiasm on display (one night a relaxed and friendly floor manager made the green servers seem charming; another day a different, vigorously proactive manager created an anxiety in those same servers that permeated the room). Right chef, wrong space? Right concept, wrong management? It’s hard to tell.

What isn’t hard to tell is that McCombe is a talented chef, and his ambition to bring elevated Mexican cooking to Melbourne is a welcome one. The problems with Hacienda are mostly in the details, and those can be tweaked. Regardless, I’ll be back for the tacos, the bone marrow and the mole, even if I have to beg for it as a side dish – with extra tortillas.