Connolly Station used to be one of the gloomiest places in Dublin. With its dark, grimy interior, litter-strewn steps and escalators and its fine arcaded brick walls painted dark blue (to go with the orange-and-black trains, presumably), it provided a ramshackle entrance to the capital, redolent of the Third World.

Anyone using the station these days must surely marvel at its slick transformation. The pointed canopy projecting out over the ramp that leads up from the junction of Amiens Street and Store Street is a mascot for what lies inside - a bright, airy concourse, sealed from draughts by planar glazing mounted on a structure of tubular steel.

Amiens Street Station, as it was originally known, had for long been the Great Northern Railway's Dublin terminus. Completed in 1846 by William Deane Butler, it was described by Maurice Craig in Dublin 1660-1860 as "a respectable building . . . coarse in detail and poorish in conception, compared to Broadstone or Kingsbridge".

Though set at an angle to Talbot Street, its Italianate tower closes the long vista from O'Connell Street and can be seen from as far west as Capel Street.

The symmetrical positioning of Connolly's campanile has been compromised by the construction of an office block behind the station, veering off towards the north-east. From a distance, this grey box looms up like a lopsided shoulder-pad.

Its location is not accidental. Because this part of the site lies within the Custom House Docks area, it carried the benefits of IFSC tax incentives and CIE had been toying with plans to cash in on it since 1987. The deal with Padraic Burke's Lowstrand Ltd, which developed the office block, paid for the station's refurbishment.

Lowstrand won the right to build the office block following a developer competition, in which architecture clearly played second fiddle to finance. Apart from a cash contribution of some £3 million, one of the few advantages was that the contractor, John Graham of Dromore, Co Down, had useful railway experience.

The new building, designed by Tony Cotter, who was also responsible for Lowstrand's multi-storey car-park on Fleet Street, is disappointingly bland compared to the sophisticated structure envisaged in 1996 by Iarnrod Eireann Architects; all they have in common is a volume of office space on three floors, raised on stilts.

The whole scheme, including the station refurbishment, was a logistical nightmare, as Connolly had to be kept open while all the work was under way. It was also designed on the basis that the existing ramp - described by Maurice Craig as the station's finest feature - would remain in place.

Though the ramp, which was added in the 1870s to provide a separate road access to the station for horse-drawn cabs, is now defaced by multiple advertising hoardings on its stone wall, it still fulfills this function rather well - even if the old cabs have long since been displaced by taxis, cars and double-deck buses.

Yet, the re-making of Connolly was barely completed when CIE's Luas light rail project team announced that its preferred option to serve the station would involve demolishing the ramp in its entirety so that trams could enter the station compound at street level. This is analogous to moving the goalposts after a match has started.

According to the environmental impact statement prepared for CIE by McHugh Consultants, the removal of the ramp would create a new public square that would open up the IFSC site to the rest of the city centre. A canopied structure over the Luas stop would also create "a focus of visual interest, illuminated at night".

This misconceived plan would make nonsense of much of the work carried out at the station. The projecting canopy would be marooned at a high level and its associated traffic island raised up and festooned with escalators, stairs and probably a lift to give passengers arriving by Luas access to the mainline station .

The smooth transition facilitated by the ramp would be sacrificed, as would direct road access to the car-park behind the station; that's why the new office block stands on stilts. If the latest Luas plan is approved, this rather dark zone is likely to be infilled with retail units - hardly a compensation for the loss of the ramp.

As things stand, the new concourse functions very well. The ticket office is just inside the entrance and close to the top of the escalators from a new street-level entrance on Amiens Street. "Everything about it is legible," says David Hughes, of Iarnrod Eireann Architects. "You can see the trains as soon as you come in."

Transparency is one of the themes. Even the control room above the ticket offices is fully-glazed, with only white ceramic lines to give those working inside a modicum of privacy. "It's probably more my vision than theirs," Mr Hughes conceded, adding that there has been a request for blinds.

E's chief architect, calls a "maintained environment". As in Heuston Station, the concourse is insulated from the train hall by a glazed partition. But unlike Heuston, there is no sense of East and West Berlin because the train hall was refurbished first, with the awful paint stripped off its red-and-cream brickwork.

A new cafebar, oddly called Oslo, is located on a metre-high podium in full view of the new digital departure board as well as the trains and the entrance. Left luggage lockers are ingeniously arranged underneath, though there have been some teething troubles with the use of revolutionary fingerprint technology.

The roof over the concourse was originally intended to be a tented structure in voguish Teflon-coated tensile fabric, but this had to be dropped when it could not be guaranteed for more than 10 years. Instead, it has been covered in Calzip - "upmarket wrinkly tin," as Mr Hughes describes it - and patent glazing.

He had a horror of using triangular trusses, not least because of the twisting geometry of the roof structure, and a diamond-shaped alternative was devised by consultant engineers Michael Punch and Partners, inspired by a scheme they had seen in Milan. It looks particularly attractive at night-time.

Not so impressive is the new entrance from Amiens Street. Despite an effort to liven it up with a kinetic lighting rig by Orna Hanly (meant to represent the Liffey from Heuston to Dublin Bay), it still feels like a grim passage. The rough-textured cement render walls, painted grey to deter grafitti artists, look cheap and tacky.

Apparently, Lowstrand's limited budget did not extend to using the same armour-coated plaster, with a wonderful verdigris colour, which was applied to the wall of the Oslo cafe-bar and the housing for the escalators; it would have worked out at six times the price. Joints between old and new granite are also quite crude.

A new DART link is also being created to rationalise what until now has been a quite labrynthine connection beneath the platforms. This has involved tacking a new structure in glass and steel onto the side of the station; as soon as it is completed, all DART passengers will use the mainline station entrances.

As for what to do about Luas, the most logical solution would be to take the tramlines from Busaras in Store Street through Talbot Place into Talbot Street, swinging around into Amiens Street in front of Connolly Station, then turning into Sheriff Street and then onwards to the Docklands area, possibly on the Mayor Street axis.

Thus realigned, Luas would link up directly with the DART/Dublin Bus interchange being planned for Sheriff Street instead of being remotely located from it. Conflict with through-traffic on Amiens Street could be minimised by building a short underpass for cars; this would also allow the creation of a piazza in front of the station.

Surely it couldn't be true that the only reasons why this sensible option has been cast aside is that the gardai in Store Street use Talbot Place as a car-park and there is a reluctance to take Luas through Sheriff Street?