It's a fairly small museum and certainly more for the junkers lovers. Outside is an east german built Il-14 (bit shabby last time) and you can see the old red brick junkers administration building.
When in Dessau make sure to see the Bauhaus Museum too and -if the weather is nice- wörlitzer park gardens with little lakes and pavillions is worth a visit too. Dessau is still an active aerodrome so just grab your chipmunk and check yourself. Easy to continue to Tempelhof VFR along the autobahn for a final visit there.