ABM, do you have a "like kind" replacement clause in your policy? If your roof needs to be replaced, they HAVE to do it and they have no choice. They're trying to buy you off. As has been said before, don't cash the check.
Call the insurance company and tell them that you don't accept the finding. Tell them you want a copy of the adjuster's report and want another adjuster to look at the roof. Have your roofer meet them there (and have your roofer inspect the roof before the new adjuster returns). Your roofer will be your advocate because the roofer will know more about roofing than the adjuster. Have your roofer write up an estimate (that will be on the high side to cover your deductable). Make sure it includes the following items:
--Type of roofing material (asphalt, wood shingle/shake, tile, slate). Make sure your new roof has a Class A fire rating. If you get a roof with a Class 4 impact rating, you'll receive a discount on your insurance (State Farm is 28% of the roof portion of my policies). Those asphalt shingles are referred to as "IR". It's a bit more expensive, but the insurance company will pay for it because it reduces their liability.
--Flashing (26 gauge aluminum is considered the standard. Make sure your chimney flashings are sealed, you may have valley flashings or you may have weaved valleys
--Underlayment. You should have at a minimum 30 lb. felt covering the entire roof. I would go further and get ice and water shield two feet above a hot wall and in every valley. Also, check out some of the manufactured underlayments (they look like housewrap).
--Decking. 3/8 OSB is generally minimum standard, but I think it sucks. If you have to get new decking, get at least 1/2" or 5/8" CDX plywood. Whatever it is, make sure there are at least some screws in it (roofing nails can pop) and that it's all the same material and thickness, otherwise it will telegraph through.
--Vent stacks and sleeves should be replaced and painted the color of your roof (GAF/Elk has a series of paints to match most roofs).
--Venting (soffit and ridge vents IMO are the best, but turtle vents are okay too).
--Gutters (if any portion of any of your gutters have a hail dent, those damaged runs have to be replaced by the insurance company). You can generally get any roofing company to give you "free" gutters for getting the job on your roof. Get the largest downspouts you can (generally 3"X 4").
You can always threaten to file a "proof of loss" claim. The second to last thing an insurance company wants is one of these things. It basically means you and your roofer puts together a claim on your roof and the insurance company has 30 days to respond to it. If they don't, the claim is awarded. You can also threaten to sue or to go to arbitration. This situation is the last thing they want. In court, insurance companies are liable for up to treble damages.
Finally when you do get your roof replaced, have your roofer take photos. If you plan to sell this house in the future, a new roof is a HUGE benefit.
Take some time to learn about roofing systems. There's a lot of information on the web. I like Malarkey (PDX based as well), but Certainteed is good (they fixed their degranulation problem), GAF/Elk is well regarded and Owens-Corning is fine. TAMKO is a little lower quality. If you use three or more products from the same company installed by one of the companies licensed installers (your guy may be one of them), you get an additional warranty from the roofing company. It's hard not to use at least three products from one of those companies (e.g., shingles, starter strip, ridge cap, etc.)
Good luck.