The nature of the NRL makes the transition tough for Super League players.
"The competition is more consistent over here. There are more good teams and each week, you're playing against a tough side. There are sides quite far down the ladder that can still win the grand final."
He was ever-present during his first season in 2014 but the 26-year-old suffered a knee injury in March which sidelined him for three months.
Tomkins will return to the Wigan Warriors, his boyhood team.
He left Wigan after winning two grand finals, two Challenge Cups and the 2012 Man of Steel award, and was the highest-paid player in the UK during his five years in the Super League.
So what's the value of British players leaving everything behind — their friends and family and all the comforts of home — to play in the NRL?
It was recently announced that Tomkins had cost $90,000 per game during his first 18 months at the Warriors — making him the most expensive player in rugby league.
"I didn't pay it and I didn't get it," said Tomkins. "That's irrelevant to me and the only pressure is to perform each week. I wanted to come here for a challenge and get better.
"It's been frustrating. I've missed about 10 games this year but I played every game last year. It's inevitable in the sport that we're in that you're going to get injuries."
Kevin Neighbour, originally from the UK, spent several years coaching in England before he worked under Rohan Smith with the Warriors' New South Wales Cup side last year, working with the likes of Tuimoala Lolohea, Charlie Gubb and Siliva Havili, who now feature regularly in the NRL.
"It's pretty different when you're kind of a nobody and start all over again. I think it's good that you can get the opportunity to test yourself in an environment like that."
The Super League announced last month they were introducing a marquee rule from 2016 which means clubs can sign a high-profile player who is exempt from the salary cap.
There's no doubt this move is to prevent the competition's world-class talent leaving to play in the NRL or switch to rugby.
Tomkins admits he's always been open to a move to rugby and former league superstar Sam Burgess looks set to feature for England in this year's World Cup.
Burgess's brothers George, Tom (both Rabbitohs) and Luke (Manly) are all still playing in the NRL after starting their careers in England and they're not alone.
More have crossed over in recent years, including Mike Cooper (Dragons), Josh Hodgson (Raiders) and James Graham (Bulldogs).
Catalan Dragons second rower Elliot Whitehead will also be joining Hodgson at the Raiders for 2016.
Former England international Chris Thorman moved from the Super League to play for the Parramatta Eels for a season in 2004.
He said: "You'd be amazed at what the crossover is like.
"We want to improve ourselves and there's nothing like travelling to the Southern Hemisphere to learn from the best."
