"We're not a very good hockey team. We've let a lot of things go that we normally shouldn't," O'Reilly said during a six-minute session at his locker Wednesday before the team's final home game of the season, against Montreal.
"It's so frustrating coming to the rink right now. Practicing. There's no purpose to it," he added. "I'm sick of losing. It's getting exhausting and it's not fun. It sucks the fun out of the game."
O'Reilly blamed the Sabres' troubles on season-long struggles with consistency and players falling back into bad habits. He also blamed himself for a failure to assert himself more in a leadership role.
"I really didn't step up and hold guys accountable and be a voice, and it's tough," he said. "I think at times I didn't say enough, and at times I maybe said too much."
O'Reilly's frustrations reflect the disappointment surrounding a team that has suddenly grown stagnant under an ambitious rebuilding plan, which began after the Sabres finished with the NHL's worst record in both the 2013-14 and 2014-15 seasons.
O'Reilly, 26, was pegged as a key fixture in the Sabres' future. Buffalo acquired him in a multiplayer deal with Colorado during the 2015 NHL draft, shortly before the Sabres selected another key building block, Jack Eichel, with the No. 2 pick.
The additions began paying off last season, when Buffalo finished with a 35-36-11 record, marking a 27-point improvement over the previous year. This season, Buffalo (32-25-12) needs to win its final three games to match last year's win total.
Though second-year coach Dan Bylsma is taking much of the heat for the team's troubles, O'Reilly said the criticism should fall on the players.
"We're the ones on the ice," O'Reilly said. "You can't look at him to take the fall. It's a lot of us. We've all kind of let it slip here."
Despite a series of injuries that sidelined numerous players during the first two months of the season, the Sabres worked their way into contention in mid-February before they unraveled. Starting with a 5-1 loss to Chicago on Feb. 19, Buffalo endured a 2-8-2 skid.
O'Reilly has been inconsistent this season, though his play was hampered by an abdominal strain which forced him to miss six games in November. He's third on the team with 20 goals and second with 53 points.
O'Reilly's frustrations echoed those expressed by Eichel following a 4-2 loss to Toronto on Monday.
"As much as I'm a young guy, I've got to take on more responsibility, be more of a leader on this team," Eichel said. "I've got to expect more out of myself."