"I unashamedly want this to be one of the best Mexican restaurants in the world," says Dr Sam Prince of his just-opened Mejico in Pitt Street. So it's 20 out of 20 for chutzpah, at least. And 20 out of 20 for the strange sense of deja vu I get standing outside on the street looking up at the bright facade.

Then the peso drops. Right next door is 2012's big success story, Jamie's Italian, where a young chef is installed in the front window busily making pasta by hand. In the front window of Sam's Mexican, there's a young chef busily grilling piles of corn cobs.

The two parallel dining universes each have a long, skinny space that starts with a lively bar area and finishes in a high-ceilinged dining hall. Where Jamie's packs in two levels of dining, Mejico offers one, but there are further parallels in the rough-brick, brightly painted industrial references, and the interchangeable crowd of party-time girls, beer-drinking blokes and after-work couples.

And I bet the guacamole service ($9) is something Jamie wishes he had invented. Order it, and a guacamole girl will arrive at your table with avocado, molcajete (Mexican mortar and pestle) and a tray of goodies. It's quite a charming experience, as she spoons the flesh from the skin, and starts pounding it while adding - to your liking - coriander leaves, red chilli, lime juice, red onion and wasabi (wasabi?). What with the theatre of it all, and the long, crisp, plantain chips that come with it, it's a no-brainer bargain for two or more to share.

It would have been more impressive had it not taken 45 minutes for Senorita Guacamole to get to our table, long after cocktails are finished, and the first two dishes have bitten the dust, but the system here is Wagamama-style, with dishes coming out as the kitchen does them, rather than when you actually want them. (The trick? Order a dish or two at a time, to get them in the sequence you want).

Swiss-born chef Daniel Schai's menu runs across salsas, ceviches, tacos and a few main courses such as glazed pork ribs. Soft-shell tacos ($16) come with shreddy, braised-and-pulled-apart lamb shoulder, and could do with a bit more brightness and acidity in the mayo-chilli-herb department. If you want crunch, go for a ceviche on small, crisp, house-baked tostadas instead. The scallop version, mixed with avocado and lime and topped with pomegranate and crisp shallots, has a good balance of richness and acidity.

There being a limit to how many times you can order glazed pork ribs in a week of public eating duty, I try the market-fresh fish (ling?), flavoured with garlic, ginger and coriander. It's coated not particularly attractively in a spicy, seedy achiote paste ($32), which feels a bit heavy-handed for the fish.

There's a side of baby-soft roasted pumpkin ($8) boosted with smoky ancho chilli and served with a little plasticine-textured queso fresco (Mexico's fresh white cheese). A nopalito salad ($9) is disappointing for anyone eager to experience cactus for the first time - you have to hunt for it in what is basically a Mexican slaw of red cabbage, carrot and tomato.

In the meantime, the music is up, the lights are down and the responsive young staff are run off their feet delivering Mexican beers and tequila-based drinks from a proudly collated tequila list. Winies will find a short but serviceable list of Spanish and South American labels, including a vibrant, citrusy Santa Vita 120 Sauvignon Blanc from Chile's Lontue Valley, which is decent value at $10 a glass and $45 a bottle.

Of three desserts, a "fruit hat" ($10) is little more than a pimped-up fruit salad and ice-cream, creatively expressed on a platter painted with a brush stroke of hibiscus flower syrup but not tasting of much at all.

As for Mejico (pronounced meh-he-co) being one of the best Mexican restaurants in the world, it's not. It's certainly a step on from the cheese-laden Tex-Mex food we grew up thinking was Mexican food, but it's a long way from the calibre of, say, Empellon Cocina in New York or Pujol in Mexico City. So, full marks for bravado, and 12.5 out of 20 for the rest.

The low-down

Best bit The joint is jumpin'.
Worst bit Gaps in service and food delivery.
Go-to dish Guacamole and plantain chips, $9.

Terry Durack is chief restaurant critic for The Sydney Morning Herald and senior reviewer for the Good Food Guide. This rating is based on the Good Food Guide scoring system.