I've never fished the Glomma, but have heard many warm reports. Basically the whole river is alive with trout and grayling. There's some very large whitefish to be had in other reaches too.
Did a quick search on google and this seems to be the best website:-
Kvennan Fly Fishing - Glomma river in Norway, topclass fly fishing for grayling!
Otherwise all the others are in norwegian. Fine for me, but a little harder for you

Try using an online translator......
By all accounts, your a lucky man.......