McLaren have not won the constructors' title since 1998.
Button added: "This is a beautiful car - many you will see will not be.
"There are some good rule changes giving the engineers and aerodynamicists something to really think about.
F1 ON THE BBC IN 2012
All the grands prix will be shown on BBC television
Ten will be live - China (15 Apr); Spain (13 May); Monaco (27 May); Europe (24 Jun); Britain (8 Jul); Belgium (2 Sep); Singapore (23 Sep); Korea (14 Oct); Abu Dhabi (4 Nov); Brazil (25 Nov)
The rest will have extended highlights - Asian time-zone races will be shown at 2pm; European time-zone races at 5.30pm
All races will be live on 5 live and the BBC Sport website
The website will have live video of the races that are live on TV and live audio and text commentary for all races
"Everyone seems positive, we will see how it is when we get out on to the track."
McLaren have also abandoned the distinctive L-shaped sidepods that distinguished the 2011 car, reverting to a more conventional shape.
Hamilton said: "The back of the car is much neater, it's much tighter. The focus was on getting it as tight as possible for aerodynamics.
"It's about dropping drag and we have tried to get as much downforce back as possible with the banning of the blown diffuser [where teams directed exhaust gases along the rear floor of the car even when the driver was off the throttle]."
He said that the rule change had made an obvious difference to the way the car feels, having already driven it in the team's simulator.
Hamilton added: "It's a lot trickier to drive now than it was but I'm sure, as we get into the season, we'll get that back."
Both men said they were looking forward to the challenge of the new season, which features six world champions for the first time in F1 history.
Kimi Raikkonen has returned to F1 with the Lotus team after two years in rallying, to join fellow champions Michael Schumacher, Fernando Alonso, Sebastian Vettel, Hamilton and Button.
"We love to have the competition and we love to have the great drivers out there," Hamilton said. "We hope there are no world champions added to [the list].
"It's great for the fans and the sport and hopefully we'll be able to put on a good show. We do have a good looking car and, when a car looks good, it generally is good."
Gary AndersonBBC Formula 1 technical analyst
This is a test car - as McLaren have been saying fairly loudly - and there will be developments coming along, but at the moment nothing stands out as a concept other teams would struggle to match. But McLaren have had difficulties early on in the last two seasons, so maybe they want to have a solid base to start from. Right now, though, there is nothing on this car that would make the hairs on the back of my neck stand up
Asked who the drivers expected McLaren's main competition to be, Button said: "The Red Bulls will be strong, they're not going to suddenly build a bad car after winning the championship for the last two years.
"Do we know where we stand? No, but the important thing is we focus on our own work in testing and in Melbourne we will find out where we are compared to our competitors."
Hamilton added: "Last year we were the team closest to the Red Bulls, that's comforting, and we improved a lot too. If we can start the season better than last year then we will put good building blocks down.
"We have the fastest rate of development, so that should give us a strong position to start the season."
Team principal Martin Whitmarsh said: "It will be close, it's a massively competitive championship. No-one in my view is going to run away with it.
"We don't like losing, coming second in the last two years has been frustrating.
"We want to win races and world championships. We have two great racing drivers, everyone can see the chemistry between them but they want to beat each other.
"There are some very strong competitors out there but we are feeling at the moment as if we are in a good place and we're looking forward to getting to Melbourne and competing for championships."
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