It will probably be about as good as new.
If you open it, the smell should be smoothing, as a gun powder junkie would say. If it has a rancid, ammonia type smell - it's garden fertilizer material - and will probably have a reddish top layer to the powder. As arlaunch advised, there will be a fine dust when pouring the powder into a container/powder measure.
I have used Hodgdon powder that was made from surplus WW2 powder and it was excellent - purchased back in the late 60's in quantity and finally used up in the early 90's. When shot over a chrony, I never saw a difference that would amount to anything except maybe the temperature of that day.
Having said all that - I did purchase a couple cases of IMR 4350 back in the mid-'70s in the off brown colored metal can with red cap. 8 pounds went bad on me after 25 years. I still had about 1.5 pounds of that powder in a plastic pill bottle container that I used/mounted on my Sinclair adapter for the Lyman 55 power measure with the Culver insert - that powder was as good as new when I discovered the remaining IMR-4350 was bad - so I and a couple others who have had trouble with that powder in those metal can containers think it was the inside coating of the can that caused the powder deterioration - of course IMR denied that assumption.