Since people are talking about hero power in this thread I figured I'd swing by and drop where I currently have hero power ranked. The list below is based off of both scrim results as well as personal theorycrafting. Below the list is some analysis as to why things have been arranged this way.
Top Tier (IE: All respectable picks in scrims with a high success rate. Generally the Heroes with the largest degree of power in the current game)
DPS - Kerrigan, Valla, Falstad, Tychus, Barbarian (she's played as a DPS)
Support - Uther, Brightwing, Tassadar, Malfurion
Tanks - Diablo, Arthas, ETC, Stitches
Middle Tier (Situational picks, lacking in the raw power of the tier above but can be good in specific team comps)
DPS - Raynor, Nova, Zeratul
Support - Tyrande
Tanks - Tyrael
Specialists - Hammer, Abathur
Low Tier (Even more situational than the above, infrequently used. Fatal flaws)
Support - LiLi
Specialists - Zagara, Nazeebo, Gazlowe
Bottom Tier (Practically never picked or used)
Tanks - Muradin
Specialists - Murky
Illidan Tier
DPS - Illidan
I think the biggest thing people might take issue with on this list is the placement of LiLi. LiLi's problem is that she's disproportionately powerful in pubs relative to her status in organized play. Organized play is characterized by both small and large combinations of hero skills that lead to people dying (ie: Uther stunning someone and a hero like Diablo then displacing them with slam --> push). Not only does LiLi lack the ability to combo with other heroes in that way, but she also has a problem defending herself against those combos. This isn't a problem for her in pubs because people rarely have good coordination on their abilities, but it's nothing short of crippling for her in a competitive environment. The end result is that she's far less valued than the other supports who can bring healing + CC instead of merely healing.
Specialists definitely have some issues in the current game. The best performing specialists are Hammer and Abathur, and that really only stems from the fact that Hammer is effectively just a slow moving DPS hero, and Abathur ends up merely cloning a regular hero in the end. I think the root problem probably stems from the fact that the game is most heavily rewarding fast and aggressive rotations with a full team of five (with good combat power) - something that tends to overly punish the attempted gameplan of most specialist heroes.
As far as Illidan goes - he's without doubt the worst hero in the game. His health and damage are severely handicapped to compensate for the theoretically godliness of his kit. As a result, he's the sword guy from Indiana Jones -
http://www.youtube.com/watch?v=Mur-c5IiWJI
I think that covers most of it.