Heading into the halfway point of the season, the Nets find themselves at 20–20 — which sounds great if you’re an ophthalmologist, but isn’t so good if you began the year with title aspirations.

New Jersey’s flaws — poor depth, erratic shooting, and an unproductive frontcourt — were known coming into the year, but it was hoped that the “Big Four” of Vince Carter, Jason Kidd, Richard Jefferson, and Nenad Krstic would more than make up for it. Instead, the Nets got off to a sluggish start, Krstic blew out his knee, Jefferson tweaked his ankle, and Carter mentally flitted in and out of games. Only Kidd held up his end of the bargain.

However, the real blame for the Nets’ struggles lies with management’s off-season complacency. Everyone could see the Nets had these weaknesses, but the team’s unusually good health last year masked many of the warts. Minus Krstic and Jefferson, they’re now laid bare. Even the good news has been tempered with more bad. The Nets have won nine of 11 games to take over first place in the pathetic Atlantic Division, but the celebration will be brief. Jefferson had to undergo surgery on his balky ankle and will miss six weeks (even that may be optimistic). Meanwhile, the schedule takes an abrupt hike in difficulty as the Nets start a West Coast trip.

So as I hand out grades for the Nets’ midterm report card, don’t expect to see a lot of high marks:

HASSAN ADAMS: B+ The second-round pick has provided a shot in the arm with his energy, rebounding, and finishing skills nearly every time he takes the court … so why doesn’t this happen more often? Per 40 minutes, Adams averages 17.0 points and 7.1 boards, and he’s shooting 57.0%. Perhaps Jefferson’s absence will give him the chance to shine.

JOSH BOONE: D New Jersey’s “other” first-rounder wasn’t supposed to provide as much immediate help as Marcus Williams, and, well, he hasn’t. Boone looks like a big-time rebounder, but has shown a frustrating inability to finish near the rim.

VINCE CARTER: A- I know it’s become fashionable to say Carter is having an off year, but anytime somebody wants to offer some proof, give me a ring. Carter’s numbers are just what they were a year ago; what’s changed is that the increased losing has made his laissezfaire approach a whole lot more frustrating. Carter can opt out of his deal after the summer and likely will. Thus, the question du jour is whether to deal him in the next month, or gamble that he’ll re-sign as a free agent over the summer.

JASON COLLINS: D-Weknow he’s not out there for his offense. But good heavens, this is ridiculous. He’s averaging 4.7 points per 40 minutes, shooting 37.4%, and has one of the lowest rebound rates among NBA centers. Defense is his thing, but bad knees limit his mobility, and his specialty of post defense is diminishing in value now that teams are playing smaller and faster. Using my Player Efficiency Rating (PER, a perminute rating of a player’s statistical effectiveness), Collins has been the least effective regular player in the NBA this season.

LAWRENCE FRANK: B Frank gets as much from his players as one could reasonably expect, especially defensively. But I’ve got to ding him for the misplaced early-season faith in Antoine Wright and the paucity of Hassan Adams sightings of late.

EDDIE HOUSE: C- House hasn’t shot as effectively as hoped since recovering from knee surgery. That’s a problem since he’s a 6-foot-1-inch shooting guard, and as such is essentially worthless if his shot isn’t going down. But we’ll grade him on a curve because of the knee, especially since he’s had a few strong games of late.

MILE ILIC: INCOMPLETE The 7-foot-2-inch Serbian rookie has hardly played, so file his name away for next year.

RICHARD JEFFERSON: A (GUTS), C (PERFORMANCE) Jefferson’s numbers were hugely disappointing by his recent standards, as the bad ankle forced him to rely more on his jumper and strangled his rebounding numbers. That said, hardly anybody in the league would still have been playing on such a bad wheel, and his ability to stay in the lineup helped keep New Jersey afloat in the first half of the year.

JASON KIDD: A I can’t see how the Nets can possibly be considering moving this guy when he’s playing so well, especially since they have no chance of getting a star of equal caliber in return. Hopefully, all those rumors were miscommunicated, and the Nets were really trying to trade Joumana. This is the best Mr. Kidd has played in four years, and if there’s any justice in the world, he’ll be heading to the All-Star Game. Per 40 minutes, he’s nearly averaging a triple-double – 15.3 points, 9.7 assists and 8.8 rebounds.

NENAD KRSTIC: B Prior to the injury, he was off to a great start, netting 20.1 points per 40 minutes and shooting 52.6%. Which takes us to New Jersey’s second-biggest dilemma of the summer — how much to offer a still rehabbing Krstic in a contract extension. If he can match this performance in the future, he’s worthy of a princely sum.

MIKKI MOORE: B+ Look what we found! An off-season afterthought that cost only a 2009 secondround pick, Moore’s infectious energy gave the team a huge lift just when the loss of Krstic had things looking bleak. He’s shooting 65.4% from the floor, and despite a lack of muscle has been surprisingly competent on the glass.

BOSTJAN NACHBAR: C Bokie finally seems to be figuring out this whole professional basketball thing, having effective moments as a power forward when the Nets go small and getting to the line with surprising frequency for a jump shooter.

BERNARD ROBINSON: INCOMPLETE The inactive list regular is only here because he’s not Jeff McInnis. Don’t file his name away for next year.

CLIFFORD ROBINSON: C- The dramatic tip-in against the Knicks aside, Robinson hasn’t played well since coming back from knee surgery, and the 40-year-old wouldn’t be a rotation player in a less tattered frontcourt.

MARCUS WILLIAMS: C- For a guy who was supposed to be a pass-first point guard, he sure likes to shoot the rock. He’s not accurate enough to be putting it up so much, either, especially from beyond the arc (28.8% on 2.0 attempts a game).

ANTOINE WRIGHT: D- Wright got a chance to prove himself early in the year, and instead proved he can’t play. He’s had some moments at the defensive end, but overall the 2005 first-rounder must be considered a bust.

jhollinger@nysun.com