Can I fix this bad beef stew?

Let's look at the factors you have enumerated as problems with the stew in its current state:

• Overcooked. By overcooked, I infer you are referring to the meat. There is essentially no way to fix this, as the cooking process is irreversible. The only thing you could do is remove the meat and start cook new meat, but that is tantamount to starting an entirely new batch of stew.
• Disintegrating vegetables. You can pick out the vegetables (if they still have enough structure), and add new ones that are par-cooked separately, but they would not have the benefit of flavoring from being stewed with the meat. This almost certainly is not worth it.
• Not enough gravy. This is fixable: just add appropriate stock and perhaps something to thicken (although the disintegrating vegetables may serve that purpose just fine). However, you will dilute the flavor of the stew.
• Under-seasoned and bland. This is also fixable: add salt, pepper, and other seasonings of your choice. It will need some time to integrate with the rest of the stew which calls for cooking, though, and as the stew is already overcooked, may not for the best.
• Metallic, canned flavor. I don't know what this refers to, and without more information on how it happened, it is hard to speculate. Still, flavors, once the are in a stew, are almost impossible to get out.

This stew has so many fundamental problems that overall it is probably practically unfixable. Any true fix would be essentially starting a new stew and mixing it with the existing one, which has texture and flavor you don't like--so why not just eat the new stew?

Sorry, you probably just want to discard it.

Right now I'm thinking of draining the whole mess and making a new gravy but if there's a way to salvage what's already there I'd try it.

Before you pitch it, I'd consider cooking it even longer -- we're aiming for 'ragoût' (cooked to rags), not just your typical stew. We want the vegetables to completely disintigrate, until they're more a thickener for the stew, rather than indentifiable on their own.

You can then serve it over pasta, rice, or a baked potato.

If you'd prefer adding back in some vegetables for texture without further cooking of the meat ... I'd actually suggest roasting them in the oven, then mixing them in. Proper selection of vegetables can also be important -- a waxy potato (like a red potato) won't break down like a starchy (aka. flourly) potato (like a russet) will. If you're going to cook them in the stewing liquid, add tomatoes or a shot of vinegar into the liquid to prevent onions and potatoes from softening too much. Frozen peas or corn can add some quick texture (canned are typically mush, and might add to the metallic flavor).

As for the blandness issues, it's hard to say. If your basic salt and pepper aren't working, reach for other herbs & spices. You could try going heavy on the paprika and thyme to make it more like a goulish, or a blend of 'italian' spices to make it more like a ragù but beware of oregano which can have a metallic quality in large amounts. Sometimes alcohol can help, like a shot of sherry towards the end, or some wine, hard cider or beer earlier in the cooking process.

For both the blandness and metallic issues, vinegar or other acidic (eg, tomatoes but not canned) or sour (eg, serving with sour cream) notes might help.

... so, to summarize :

• Option 1 : cook longer, re-season, serve over rice/pasta/etc.
• Option 2 : re-season, add roasted vegetables and/or frozen peas or corn for texture.
• Add tomatoes, vinegar or sherry to brighten the flavors
• Serve w/ sour cream to mask metallic taste.

It actually sounds like it may under-cooked. The veggies may be soft and dissolving and the meat may be fully cooked and tender, but the stock has not boiled down and had time to develop flavor. If served too soon the vegetable flavors can be a bit tangy or metallic. An hour is really not enough time for a pot full of stew. I cook for at least two hours.

If I want some of the vegetables to hold their texture a bit more then I will add them at different times. I always add onions first because I want them to nearly melt. Then soon after I add carrots soon because I only like carrots if they have been cooked until they have almost no texture left. I hate the flavor of raw carrot. I add tomato pretty early on because I want to reduce a lot of the water they add. I add potato about half-way through because I like them to have a bit more structure left when I serve the stew. With celery I add half near the start and half with the potato because I like both the soft, mushy celery and the slightly crunchy celery. Usually I cook a stew for about 2 hours. The last hour I have the fire as low as I can get it and have the stock barely bubbling with the cover off. The fluid should drop about 1/4th volume. I like to have the stock cook with most of the salt it will need, but this can be hard to estimate when I am out of practice. In that case I aim low for the salt and then add most near the end after the stock has reduced. It's safer this way. For me, it isn't beef stew without red wine. I add 1/2 to a whole bottle of red wine early so it has plenty of time to reduce.