On Monday morning, the new Sydney Metro City line officially opened its turnstiles to the public, attracting tens of thousands of Sydneysiders to use the service.

After a delayed start, it's proven popular, with more than 1 million passengers boarding since its opening, and 99 per cent of services having been on time.

Friday night had the biggest take up so far, with 64,000 people using the line from 5pm until the last service.

The patronage has "exceeded" expectations, according to the government.

But while the service has been efficient so far, with today's Sydney Metro Open Day closing this inaugural week, has it been a success?

First week a success, expert says

According to Geoffrey Clinton, a senior lecturer in transport and logistics management, the answer is yes.

"At this stage, it certainly seems like a big success for Sydney," he said.

"It's become integrated within the rest of the transport network. It seems to be popular. There's been no major issues with it."

Dr Clinton said there was a number of reasons for that popularity, including the appeal of something new as well as how the automated service feels like something "that's exciting, that's modern and futuristic".

But Dr Clinton added that another appeal is how the metro creates another option for people travelling across Sydney Harbour.

"It's something we usually don't prioritise, simply because we're too busy investing in adding extra capacity where it's needed," he said.

Premier praises Metro Line

At the official opening on Saturday, Premier Chris Minns called it a "world leading infrastructure" which had given the city a new lease on life.

Flanked by former premiers, Dominic Perrottet and Mike Baird, Mr Minns acknowledged their role, along with the more than 50,000 workers, in bringing the project to life.

"Jo [Haylen, transport minister] and myself felt it absolutely necessary to pay tribute to and credit the previous government for the work that they did to bring about this Metro. It's an enormous undertaking," he said.

"One of the things that's interesting about this project is that because Sydneysiders were not able to judge the progress of it, it was all happening underground.

"I think many people were surprised about how spectacular, fast, how quick it is, how exciting it is …so what a lucky, happy surprise."

Mr Minns said former premier Gladys Berejiklian had been invited but could not make it due to a prior commitment, but he was sure she would "enjoy it in the days ahead".

Loving it, amazing, brilliant, commuters say

Those commenting on ABC Sydney's Facebook and Instagram pages echoed Dr Clifton, noting the speed and ease of travelling into Sydney's city centre.

Loving it! Don't miss that changeover at Chatswood. Shorter walk from Martin Place for me also. A little confusing with which exit to take at Martin Place but have figured it out now. It's excellent! — Elisabeth

Amazing! I live on the North Shore line and travel to Central [station]. So fast, efficient and safe, I wish the whole train system was metro! — Simone

Love it!! Takes 10 minutes off my commute to work so will be early to the office every day (perhaps!) — Joanne

Brilliant individual stations. Art is excellent. — Greg

The Sydney Metro has been so great, was also an amazing way to meet new friends with the metro nerd meet-up that happened on Monday. — Veronika

I had a quick trip today to experience it. It was good — just like being in Singapore. — Margaret

Crossing the harbour has become a non-event. — Toi

Better than I thought. — John

But some challenges getting on board...

Not everyone has found the metro to be a positive experience, with some being affected by changes and cuts to bus routes in the city's north and north-west.

My once-direct bus routes from Crows Nest have all been cancelled so this has actually added 35 minutes to my commute time as I live 15 mins walk from the station and the Martin Place Station is another 10-minute walk from my office. I'd really like some direct to city bus routes added back to the city as having to bus/train from Crows Nest is frustrating! Buses are easier with prams and for the elderly and should still be an option! — Sarah

Others have found challenges getting to the new metro, or transitioning to another train line.

Escalators are great at new stations but no escalators at Sydenham where T3 users have to go up and over to get to the Bankstown line — Nick

Good, but not enough parking at the Metro stations — Nathan

The next stage won't be painless

Some Sydneysiders may also have a sense of anxiety over the planned metro extension to Bankstown over the coming 12 or so months, Dr Clinton said. 

He said that anxiety may come from how the development could impact their existing commutes.  

Dr Clinton pointed to the building of the light rail in 2000 and the metro services in 2015 as historic examples.

Those developments, however, could hold the solution to mitigating those concerns, with how governments communicated to the public.

"For the time, until they close down the Bankstown line, I think the government needs to be working on that — getting that message out to people about what are the alternatives and how they'll make sure that people get to work."

But in the long term, Dr Clinton foresees the metro eventually becoming ingrained in normal Sydney life.

"People will will be using it. And six months from now, they'll have forgotten that there ever was a time when there wasn't the Metro there," he said. 

"People get used to it. And they build it into their lifestyle plans."