By Matthew Geagan, CBS Boston

BOSTON (CBS) — A disappointing and frustrating season by the Boston Celtics has mercifully come to an end. Boston’s season is over after a Game 5 loss to the Nets, a game that Brooklyn didn’t play particularly well for long stretches.

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But the Celtics lacked the talent and manpower to compete with a juggernaut like the Nets, and an extremely forgettable and regrettable campaign is now over for Boston. Injuries certainly didn’t help the team’s chances throughout the season, but it too often felt like the Celtics just didn’t have the fight and grit in them. Now they’re out of the mix before the second round for the first time in a long time, and they have some issues to address in the months ahead.

“We never got a true look at this team this year, but I think we have enough info that shows that we need to get better,” Brad Stevens said after Game 5 in Brooklyn. “I commend our guys for staying together. They gave us unbelievable effort and were super coachable. Jayson went to another level again — I don’t know how many more levels he can go to.

“There are a lot of encouraging signs and things, but there is the reality that we have got to improve,” added the Boston coach.

The team was bound to take a step back after the off-season departure of Gordon Hayward, but there was at least some hope that they’d maybe make a surprise run in the postseason, thanks to the continued rise of Jayson Tatum and Jaylen Brown, and a healthy Kemba Walker. They even showed some promise with a 7-3 start to the season.

Any and all promise  — from that start and throughout the season — proved to be false hope. The Celtics were only consistent at being inconsistent. After that solid start, they stumbled and flirted with .500 for most of the season, finishing 36-36. The Celtics lost at least three straight five times during the season, and their longest winning streak was six straight in April. That was followed up by the team losing 10 of its final 15 games to fall into the play-in round.

The Celtics either forgot how to play team defense or just didn’t care, finishing with a laughably average defensive rating of 111.8. You don’t even want to know what their rating was against the high-powered Nets in the playoffs. It was all a far cry from the defense-first teams that Brad Stevens had led the last five years.

While Tatum and Brown reached new levels of stardom, Walker was never healthy. And if he was, he wasn’t all that good. The season ended Tuesday night with Walker on the bench, unable to play in Boston’s final two games of the season because of a knee bruise he suffered in Game 2. It wasn’t even the knee injury that the Celtics went through loops and hoops to manage throughout the regular season, and that’s a big concern, considering Walker is Boston’s highest-paid player for two more seasons.

One of the most intriguing storylines during the season was how Danny Ainge was going to use that massive TPE that he received from the Gordon Hayward sign-and-trade with Charlotte. There were dreams of Harrison Barnes or Aaron Gordon at the trade deadline. Instead, the Celtics ended up with Evan Fournier, who was never really comfortable in green. A COVID scare followed by an actual bout with COVID kept him out of the lineup upon his arrival, and when he was in there he was never the three-point threat that he was in Orlando. Now he’s a free agent, and Ainge pretty much has to bring him back (or work out a sign-and-trade) to save face with his TPE investment.

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That was just one of the many moves that Ainge made which simply did not work out. His offseason acquisitions of Jeff Teague and Tristan Thompson were regular season disasters, though Thompson turned things around and muscled his way into five games worth of a good postseason.

Ainge, plain and simple, has to do a lot better this offseason, even with limited wiggle room under the cap.

The Celtics president has a lot of tough decisions to make. Or rather, he has some begging to do. Will anyone take Walker off his hands — and what will he have to give up to help that happen? If Kemba stays, what does that mean for the future of Marcus Smart? And is it time (gulp) to break up the promising foundation of Tatum-Brown? Trading either would be silly, especially Tatum, but you have to give something up to get something good. Anything is possible over this summer.

“I don’t think it’s nothing to stress about,” Smart said after Game 5. “We probably have a lot of fans and people on the outside thinking this and that, but three of the last four seasons we went to the Eastern Conference Final and to the playoffs [the last six years]. We didn’t have a full team and it affected us. I think we’re alright, but it’s not my decision to make.”

That attitude won’t sit well with most Celtics fans. But at least there were still bright spots sprinkled here and there throughout an otherwise discouraging season. Tatum is rounding into superstar form, evident by some absolutely brilliant offensive performances late in the season, including 50-point explosions against the Wizards in the play-in round and Game 3 against the Nets. If Tatum hasn’t reached superstar status yet, he’ll be kicking down that door next season.

And it’s hard not to play the “What If” game with Jaylen Brown’s season-ending wrist injury. Brown brought his game to a whole new level this year, adding a mid-range threat and even more explosiveness to the basket to his repertoire on offense. Brown kept the Celtics going during Tatum’s COVID absence early on, and his leadership off the floor is unmeasurable.

But aside from the two young stars shinning bright, the rest was pretty dim for the Boston Celtics. And now the season is over at the hands of the Brooklyn Nets, the same franchise that Danny Ainge fleeced eight years ago. The tables have turned, as the Nets — with Kyrie Irving — look like they’ll be contenders for the foreseeable future.

Boston’s future is a complete mystery, though it looks like they could find themselves in NBA purgatory; not good enough to contend for a title, not bad enough to contend for the best draft spots. Big changes may be on the way, but it’s just as likely Ainge keeps the band together for another chance to show what they can do if they can all stay healthy.

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The future is likely full of surprises, though unfortunately for the Celtics, they probably won’t be the good kind of surprises.