If you look at most post draft grades you will see that the majority of teams are getting A and B grades with a few C's and hardly any D's or F's. The reason is because in most cases they either drafted great athletes, filled huge needs (preferably with at least decent talent) or got extremely good value. These grades are based on college performance obviously but also on how the players perceived fit with the teams current situation based on that talent, need and value. These grades are not necessarily predictions of what the player will do although in many cases very high expectations can factor in. Unless a GM total messes up they are given a huge benefit of the doubt. Since we have no way of knowing how well a player will pan out most evaluators tend to look at the positives for most picks and assume if not best case scenario at least some degree of success based on college career and perceived fit with the team. Those who focus on stuff like "the Packers needed a WR and they didn't trade up to get one in round 1 so their draft sucks" are incredibly myopic. They are ignoring the big picture and focusing on one small aspect. In three years when we can "really judge" a draft class we are judging them on how they performed at the pro level thus far. Not only does a day after grade provide a base line as Reuter says, it is based on totally different criteria.I like the way Chad Reuter (nfl.com) puts it regarding immediate post-draft grades.
(FWIW, he gave us an "A" for Day One, "A-" for Day Two, and "A" for Day Three, with an overall grade of "A")
Of course there will always be a degree of personal bias as well. Chris Simms had Watson rated as his #2 WR in the draft. His grade of the Packers draft or at least the Watson pick, will likely be higher than someone who thought he may have been borderline 2nd round talent.
Pretty much every one of the lower Packers grades I have seen cites not drafting a WR in the 1st round and that's about it. Its all about what they didn't do rather than what they did. If they do mention Watson its usually with the caveat that he came from a smaller school and could turn out to be a star in a few years. I'm going to go out on a limb and make my bold prediction for the season. Christian Watson will have better stats than at least 2 of the WRs drafted ahead of him. That may not be much but when you consider how many people think it was a huge mistake to pass on one of the top 4 (London, Olave, Wilson and Williams) to me its saying a lot.