Clachan, Cairndow, Argyll (01499 600 264). Meal for two, including drinks and service: £80-120

If there's one thing guaranteed to encourage an appetite it's wrestling with a live 6kg halibut, while standing in a boisterous wind off the Atlantic on one of those Scottish islands which serves as the last westerly rock before the Statue of Liberty, while not wearing quite enough clothes, because you're a southern git who doesn't understand what real weather is.

Mind you, it was a beautiful halibut: as sleek as a fighter plane, as slippery as a well-oiled baby. We had been filming on the island of Gigha, at a high-end fish farm that looks like something out of a 1970s episode of Doctor Who – all steel gantries and concrete channels. Once I'd returned the fish to the water and wiped the slime off my chest, I started looking at the maps on my phone. I felt we deserved a reward. I found one.

A mere ferry ride and 90 minutes' drive away, skirting the lochs down towards Glasgow, was the restaurant of Loch Fyne, the renowned oyster farm and salmon smokery. The 40-strong chain of Loch Fyne Seafood & Grill restaurants grew out of this farm. While they license the name and supply oysters, mussels and salmon, they no longer own them. The only one that's theirs occupies a low-slung building overlooking the waters from which they take their name.

Well, it would have been rude not to. After all, happenstance can be the parent to the very best experiences. It's the long-planned excursions, the ones invested with dollops of anticipation, which are engineered to disappoint. We drove excitedly, gawping at the peaks and the steel ripple of the waters and dreaming of the best shellfish, shown off to its best advantage. We dreamed of an extraordinary moment, snatched from an already extraordinary day.

And it almost was. The Oyster Bar may not be much to look at from the outside. I'd even call it ugly and blunt. But inside all is light and bright and white and Scandinavian and Hobbit-hewn. There's lots of fish art on the textured walls: some lovely, some to be filed under "What were they thinking?" There's a fine display of prime products available to buy to take home; tables are attended by a well-drilled team of staff who manage to be professional without being dull and lifeless. Just avoid looking through the windows too closely; in the way of too many lochs the shore here is heavily crusted with rubbish.

It could all be so lovely. If only it wasn't for the details missed, the victories unsnatched. As good seafood should, it costs to eat here. For that you should be able to expect unstudied greatness; a class act in all things. Not a class act in a few things. The bitter leaf salad needs to be properly dressed. You should not stare at the chips, wishing they had spent another minute in the deep fat fryer so that they rustled against each other, like thighs dressed in taffeta. You should not let out a deep sigh over some of the fruits de mer, or purse your lips at the smoked salmon selection.

But let's talk up the good stuff. After a morning being slapped by a quite understandably pissed-off halibut their take on that classic soup Cullen skink is a marvellous thing. It's a well-dragged-up version, the potato diced just so, to tiny cubes, the chives sprinkled hither and yon. But there is still a big hit of cream and smoke from the fish. A non-fish starter of whipped goat's cheese with quarters of pickled beetroot, fresh figs and curls of walnut toast shows attention to detail. A halibut burger brings a solid square of fillet breaded and deep fried so that the flakes fall away from each other given the opportunity, all slapped between a prettily glazed brioche bun. Fat scallops, coral intact, are well cooked and partnered with Stornoway black pudding, which can never be a bad thing.

But then there are all the question marks. The smoked salmon selection is striking for being on the "I've never liked you" side of ungenerous for £12.50, especially given that one of the three is in the form of an unadvertised pâté. Pâtés are a brilliant way of using up bits of fish you might not otherwise be able to sell. The sliced salmon is good. There's a firm texture and it hasn't been cured to within an inch of its life. But it's just stingy. The smoked salmon selection in the Loch Fyne chain costs around £8.75 and they have to ship it in. Here, the salmon comes to them from farms on the loch and is smoked in a building behind the restaurant.

The £36 fruits of the sea selection has a lot of good things: the well-cracked crab, the langoustine, the single fat scallop, the perfectly serviceable rock oysters. It's odd that you have to ask for mayonnaise with this. It is absolutely vital – for the big pile of mussels, which they farm themselves, taste of nothing. It's like chewing on gum that someone else has had a good go at first. It's pleasing to see cockles there. A good British cockle can give a hoity-toity clam a run for its money, and at a fraction of the price. But these, too, are lacklustre. They should give you a proper briny slap, not just a wipe down.

Is this nit-picking? No, not when the bill can easily slip past £120 for two. Dessert saves honour. A cool lemon posset comes with a warm layer of lemon curd, which is a neat trick. A chocolate pot with crème fraîche and honeycomb is on exactly the right side of rich. It is finishable. A warm treacle tart is a fine specimen, though there is little sign of the advertised Glengoyne whisky.

To one side is a picture window that looks out at the snow-capped peaks. We watch as the clouds darken and descend. Then the weather powers towards us down the valley. Soon the mountains have disappeared from view completely and we know it is time to go. We get back in the car for our drive down to Glasgow.

The Loch Fyne Oyster Bar is no newcomer. It's been here in one way or another since the 1980s. And nobody should doubt the slickness of its operation. They know exactly what they're doing. I just wanted what they were doing to be its own kind of perfect. And right now it isn't, not quite.

Jay's news bites

■ For another eating experience with a great view over water try JoJo's on the coast road above Whitstable in Kent. It's a tapas restaurant with a roaming Mediterranean brief, which embraces dishes from Spain, Italy and the Middle East. Chef Nikki Billington has many talents, not least her pitch-perfect skill with the deep fat fryer. Her greaseless calamari are about as good as it gets. She also does a fine line in grilled sardines to be eaten staring out to sea (jojosrestaurant.co.uk)

■ A new distillery is to bring spirits production back to east London for the first time since the Lea Valley Distillery closed early in the last century. The East London Liquor Company, located not far from Mile End, will produce gin, vodka and whisky, and have a cocktail bar on site (eastlondonliquorcompany.com)

■ Grotesque excess of the week: New York's Beer and Buns burger bar has just launched a $250 Kobe beef burger with foie gras sautéed in Sauternes, white truffles and caviar. Yum! Fishy beef. If you see anybody choking on one forget all you know about the Heimlich manoeuvre.

Email Jay at jay.rayner@observer.co.uk. Follow Jay on Twitter @jayrayner1