For the purposes of this exercise, I'm going to rate players on where they play in Paulo Sousa's system, rather than where their "natural" position might be. Obviously, you're more than welcome to correct me in the comments; that's what this is all about, right?
Ciprian Tătăruşanu: B. The Romanian number one has had a solid year in goal for Fiorentina. His distribution is spotty and he's prone to the occasional gaff, but his positioning, shot stopping, and aerial presence are quite good.
Luigi Sepe: C. The Napoli loanee has made a couple of spectacular saves, but his distribution from the back is catastrophic, and the defense looks leakier when he's between the sticks, which maybe isn't all his fault, but is still kind of damning.
Overall: B-. Tata's a good and steady presence, but not much more than that, and there's not real depth behind him.
Gonzalo Rodríguez: A-. The new captain has been his usual excellent self in the back, organizing the defense and marking opposing strikers out of the game. His ability to hit long passes from the back to vary the attack is also a crucial component of the team's ethos.
Davide Astori: B+. Started off looking like a world beater, but fell off just a bit after the first month. He's still been well above average, though, and his long passing takes a little pressure off of Gonzalo when opponents press the defense.
Facundo Roncaglia: B. Facundo's actually had a brilliant year, consistently shutting down his side of the pitch; look at where opponents' goals come from, and they're nearly all from the middle or down the left. Unfortunately, the Argentinean is still prone to the occasional moment of madness, which pushes his rating down. He never complains, which makes him a better depth option than starter.
Nenad Tomović: C+. Nenad's been his usual, deeply average self this season. His positioning is suspect and he offers nothing in attack, but he's a decent tackler and surprisingly stout in the air. As a starter, he leaves something to be desired, but he's an adequate reserve.
Federico Bernardeschi: B+. Would be higher, but he still loses the ball way too often, even on his good days. Still, though, his energy, directness, and incisive passing have made him one of the team's most important attackers, and he's only going to get better. A move farther forward might suit him, so he wouldn't have to worry as much about his defensive responsibilities, though.
Jakub Błaszczykowski: C+. He's simply missed too much time to deserve a higher rating, and has been a bit anonymous when on the pitch. A lot of that is probably due to a new team, new country, new position, and new tactics. When he returns (maybe this month), he should work his way back and hopefully improve.
Gilberto: D+. Coming from the second tier of Brazilian football, we all knew it was going to be an adjustment period. He's shown occasional flashes of competence, especially against Chievo Verona, but probably needs a loan to Serie B for a year or two before he's ready to contribute. Not judging his potential here (he could wind up being a pretty good player), but his performance thus far.
Ante Rebić: C-. Maybe the most frustrating player in the squad. His defensive workrate is unreal for someone who's supposed to be a striker, and he's willing to put his head down and beat his man. However, his penchant for horror tackles and trying to do too much is infuriating; a move away on loan and regular action should help, since he always looks like a young player trying to prove that he belongs.
Overall: C+. Berna's brilliant year keeps this from going lower, and considering that youngster is playing out of position, this is a pretty clear problem spot.
Marcos AlonsoB+. I'm going to catch some flack for this, but Marcos has been fantastic. 2 goals, 3 assists, and some consistently dangerous crossing are nothing to scoff at, and his defensive contribution has been steady, as well. He's not as incisive as one might like, but he's shown an ability to dribble past his man enough to keep defenses honest. Not a star, but a vital cog in the Sousa machine.
Manuel Pasqual: C+. Starting to look his age, although it may be the knocks he's picked up. Still the same old Manny, trundling forward to spam crosses into the box. Still hopelessly over-matched defensively. His inability to finish a game is worrying, though, and we could be entering the twilight of his career.
Overall: B. Marcos has been great, although Pasqual's decline is a cause for concern.
Milan Badelj: A-. Never seems to do that much, but the team looks helpless when he's not playing. He settles everything down, providing the fulcrum that the rest of the team rests on. Right now, he's the most irreplaceable part of the squad, even if nobody notices what he does.
Matías Vecino: B+. His nonstop motor in the middle is vital to pressing and passing, as he closes down opponents and moves into space for 90 minutes every game. He's covered more ground than any other Viola player, and consistently packs every statistical category. If only he'd occasionally score from his ambitious shots from distance, he'd be unreal.
Mario Suárez: C+. Has had a few good moments, but looks lost in a possession-based midfield. The goals and dribbling have been unexpected pluses, but it's clear that the big Spaniard is better at spoiling play than fostering it; it's no surprise that he's rumored to be on the outs. Just like his namesake Mario Gómez, he looked like a perfect fit, but it's jut not worked out.
Joan Verdú: C+. He's been better than anyone expected, but still seems best suited as a substitute to bring in when his team is winning, since all he does is keep possession in a rather unthreatening fashion. Maybe he's adjusting to the faster pace of life outside the Emirates, and he'll improve in the second half of the season, but it seems unlikely.
Overall: B-. Maybe a bit harsh, but as Badelj and Vecino gel, they'll improve. The lack of solid options behind them is a definite concern, though, especially as fixtures start to pile up.
Borja Valero: A-. What a difference a year makes. Borja is back to his usual understated, brilliant, and elegant self, moving the ball quickly into dangerous positions with minimal fuss. He's occasionally been taken out of games by some, er, very physical play, but he's been at peak form for nearly the whole season.
Josip Iličić: B. Another very up-and-down player; his calling card is and has been stretches of anonymity interspersed by moments of genius. The goals and assists are superb, and he's even shown some effort on defense, but he can still drift out of matches sometimes.
Matías Fernández: C. Just hasn't played enough to justify a higher grade, and has looked hesitant on those occasions he gets onto the field. The brilliant midfielder we saw last year is still in there; let's hope Sousa finds a way to bring him back.
Overall: B. It's been pretty dang good thus far, but this is an awfully thin unit, even counting other players who can fill in as necessary.
Nikola Kalinić: A. The Croatian poacher has been a revelation. His holdup play, aerial prowess, and (mostly) assured finishing have been crucial to the team's success thus far. He's been everything we wanted Marione to be, and for a fraction of the cost.
Khouma Babacar: B+. The only thing that's kept the youngster from a full-time role is the depth chart. His goals-to-minute ratio is unreal, and he's been a good Plan B when necessary. Also, his commitment to the club is heartwarming, and he's only going to get better.
Giuseppe Rossi: C. Ugh. I don't even want to do this. Yeah, there've been glimpses of the world-class striker we love, but he's mostly been immobile and anonymous. His body seems to be fully functional, but his mind is hesitant and moving slow. He probably needs regular minutes to really make it all the way back.
Overall: B+. Depth, different playing styles, and quality. That's pretty much all you can ask for.
So, what needs reinforcing? What's pretty dang solid? Which of these grades did I hopelessly ruin?