You're right, it's impossible to grade the draft accurately the week it happened. Come talk to me in 3 years.
That said, the Saints did well. They didn't address the media opinion of what their needs were, but they addressed some real needs with the draft.
Robinson will add depth to an already very good secondary, and give flexibility if Darren Sharper continues to play games over money (not putting him down, he should get max value for his skills as a UFA - but no one is going to pay him like he's 24 when he's 34), giving the team a chance to move Malcolm Jenkins to FS (where he will shine) and have a solid nickel CB ready to roll.
Charles Brown will be a starting LT eventually, and allows the team to tell Jamaal Brown to $4!7 or get off the pot. If J. Brown doesn't get right with the team, they can trade him for value (everyone needs a LT), if he does, then they have depth at OT, which is always a good thing.
Jimmy Graham is a project guy with a lot of potential. I think he's going to develop into another Shockey or better. BIG kid, good speed, good hands, GREAT attitude. Not a lot of experience, but so much talent. If he shows up this coming season, it will cause a LOT of headaches for opposing defenses - imagine TWO Jeremy Shockey's in a 2 TE set...are they REALLY running the ball? Or are they about to burn us with a pair of TE's that our LBs and safeties don't have a chance to cover?
Al Woods is my question mark. Lots of physical potential, but unknown attitude and drive. He showed flashes of brilliance at LSU, and stretches of "meh". If he can live up to his physical potential, next to Sedrick Ellis in the middle of the D-line, it'll definitely affect the ability of opponents to run the ball well.
Tennant is a solid center, he won't need to be ready to start right away, as Jonathan Goodwin is still in his prime at the position and still playing well. But, depth is smart, and eventually Goody will have to step aside, this pick could be setting up his successor. Tennant was runner up for the best center in college football last year, so he has talent.
Sean Canfield seems to be a "toy" for Payton to play with. I doubt that either he or Chase Daniels will end up being the #2 QB next season (I'm expecting the team to go pick up a vet for that job), but one of those two will be competing for the job as Brees' protege, someone for Payton to groom to run his system, and learn from the best at how to actually run it on the field. Long term, this could be a big pick, but we won't see anything from this guy for a few years.
What I'm really tweeked about is the UDFA signings, I see a lot of good talent in there. Specifically, I like the signing of Clint Gresham out of TCU - he's a long snapper, and he's a GOOD one. A very overlooked position on the team, a good long snapper matters in every game, and this kid will make the roster. He's the only guy I've ever heard of that WORKS at it constantly, I saw a video on him that was pretty amazing - he's got incredible accuracy and gets the ball back to the kicker or holder FAST. I liked them picking up Harry Coleman out of LSU as well, he's a "tweener" SS/OLB who could be very valuable on nickel and dime packages - he's fast enough to cover RB's and TE's, big enough to handle them if they get a catch, and a real threat to blitz and lay a QB on any snap. Also, Brandon Carter from Texas - he's a giant of an OG, 6'7", 344, and has good feet.
Not an A+ with a star draft, but it is a solid B+/A- with potential for a better grade in time. Definitely a draft with an eye on the future, not the immediate return.