The first issue is which Edler thread to put this in...
Alex Edler is by far the best offensive defenseman on the team. His skating is very good. No one on the team can spring a breakaway like Edler. He has a great shot but the vision not to use it all the time. He has an off the charts offensive IQ.
Defensively, he generally doesn't get out of position (as much as Bieksa or (obviously) Ballard), but doesn't aniticpate the play as well as Hamhuis. He can lay the body as well as anyone on the back end, but conserves this ability. He is big, and while he doesn't play huge, he is no wallflower. This restraint can frusturate fans, but we've seen he can bring it and he doesn't waste a lot of time needlessly in the penalty box.
He is, in short, the most complete defenseman on this team. And he is 26 years old. While he is not yet that #1 that can anchor a defensive unit, eat up 27 minutes per game, and allow a team to carry a barely-NHL-competent #5-7, I don't rule that out of Edler's potential and his downside for the next 6 or 7 years (absent injuries) is what to get the player we see today. And that's a very, very good player.
The criticism, near as I can tell, is that he made some mistakes. People wanted Kevin Bieska's head on a pike after the Chicago series in 2010 for the same reason, and many rumored him gone. (At that time, I had my frusturations with Bieksa, but thought the Canucks might be getting a better long term value from him than Ehrhoff and suggested that if the Canucks wanted to move a defenseman for a return, it should be Ehrhoff.) If that Canucks were to have lost to Chicago in the first round of 2011, it would be Hamhuis, whose normally cool play experienced far too many blips (that came back in goals against).
In the 2011 series against Nashville, Suter couldn't contend with the Canucks pressure and was overstretched. He was a very good player then as now, but far from perfect. His turnovers led directly to goals. Look what he got paid! Drew Doughty is another -- he quality defenseman in all zones that can do many things exceptionally well, but his play and confidence does result in errors.
Few are perfect; many whose value comes as a function of assisting the offense from the defensive position do so by taking well-timed risks. I think Edler's play is entirely in line with reasonable expectations and he is a core player.
Alex Edler will make at least $6 million per year on the FA market absent material changes in the CBA. The Canucks would do well to lock him up for $5.5 million now if that's an option.
As far as trading him, it is always reasonable to consider a player in a deal; it is all about the return. Interesting to see Weber's name mentioned, as my earlier comments on obtaining Weber have noted that Edler would likely have to be the critical piece in return.