I have to tend to agree, but other people here are making a few really important points. Heavy is good at sustained damage and area control definitely, but there are few problems concerning his strengths. While I agree that the Heavy is a great Sustained damage and Area Control class, Damage Sponging and Crowd Control are pretty lacking for the Heavy right now.

First, Damage Sponging. This is a difficult thing to call a strength, particularly when there are random critical hits enabled on all official servers. What we sometimes forget is, that while 300 health is a lot, the damage (and one-shot mechanics) of other classes outpaces the Heavy's health pool pretty significantly, almost to the point of negligence.

Crowd Control. I've never really seen this as a strength of the Heavy. Sure he is, in the sense that he can zone out certain areas, but the distance-damage falloff is so significant it means very little. The fact of the matter is that other classes do a better job at Crowd Control then him (airblast, sticky bomb zoning, etc).

I think we all agree that the Heavy does have certain advantages, but I think the problem lies in the fact that the Heavy's advantages can be countered really simply, and in too many instances. Scout getting you down? Go Soldier or Pyro to deal with his high mobility. Demoman being frustrating? Jump around his grenades with a scout!

But if a Heavy is causing problems? Sniper, Spy, Soldier, Demoman, Scout.. even Pyro has a half-decent option in the Backburner.

I think what other people have posted about complimenting his strengths and weaknesses by bringing them to there extremes is a good solution. Make a Primary or Secondary that allows the Heavy to go into a sort of "Artillery Mode", where he would not be one shot by Snipers or Spies (although two shots seem reasonable), but make him unable to move while in this stance, and unable to be ubered or recover ammo. This gives the Heavy a reasonable strength in objective control that other classes don't have (Stickies can be shot, Sentries can be sapped), but doesn't make him invincible because he will have to move, particularly if there's a spy who's managed to get close (think "Spy's sappin' my Sentry!" panic) or have to move if a Sniper gets into an effective position to pelt him.