This for me is a difficult question, because it feels like we already have quite a few of the players required to excel - yet this season showed that we have some fundamental problems and lack depth.
Firstly, we need to replace Demba Ba, Peter Lovenkrands, Leon Best and Shola Ameobi. One starting striker and two or three of serviceable quality at least one of those young and with promise.
With Coloccini unfortunately looking to be gone bringing in a good communicator and reader of the game at the back is crucial. Though Taylor and Mbiwa have not had much of a chance as a partnership the early signs do not look good and so that senior experienced defender is required.
In our fullback positions we're in a decent position, even with the re-injury of Ryan Taylor's knee. Debuchy has had a horrible start here, but I'd like to think that he'll therefore be doubly keen to prove himself in the toughest league in the world next season. Santon lost interest in the second part of the season, when the going was rough but before that he contributed quite well. Defensively he has a lot of room to improve. Haidara looks to be an excellent player IMO. Favours his left, so will push down the wide channels and can whip in powerful dangerous crosses. Defensively he's quite strong and is relatively quick. Between these three we should be able to put out a soild set of fullbacks. Perch looms as the emergency fill in, and with a new central defender or two on the way (in my plans) Mbiwa can also move into a wider position in a pinch.
Our midfield is somewhat perplexing. We've seen Tiote at his best - making the simple passes with amazing consistency, breaking up the opposiing play and offering an effective shield to the defense - and also this season at his worst - shooting ridiculously from distance over and over, attempting impossible passes and dribbling himself into trouble. If he can somehow be coached back to being the effective defensive midfielder of old then it's well worth putting up with his more than occassional silly challenge. If not - then I don't have any more time for him. Cabaye is somewhat similar - at his best he's capable of striking the ball with precision and picking out inch perfect passes, but at his worst he's disinterested and lazy. I hope that we've seen more of the latter this season because he's not been fully fit and because of the negative predicament we've found ourselves in, and therefore with a clean slate next season we can see him return to a more consistently high level. Having the afforementioned workman Tiote alongside him feeding him the ball will certainly help.
Out wide and creatively HBA is an exceptional player. Used effectively he's an unstoppable game changer. Hopefully he's still here and remains injury free. I like the look of Gouffran, quick with fast feet and a pretty good footballing brain, we could do a lot worse than him. Obertan has outstayed his welcome. Marveaux is frustrating. anmd as such can't be relied upon. Best used I feel as an option off the bench. Like others have noted we do lack a wide midfielder with crossing ability - so the addition of one to compliment our new strikeforce would be nice.
In goals, Krul is good. Elliot has promise (good distributer) but strikes me as lazy. Carrying more weight than a professional footballer should IMO.