Looks like a decent trail. OK for cross bikes (assuming it's dry)?

Sure thing - I've been riding it on the gravel bikes for years. It definitely is not good when wet and there is frequent flooding during a wet Spring but you can go around those sections by road. Ottawa to Marseilles is the section most likely to flood. Downed trees can also be an issue. The state seems to do almost no trail maintenance, even though it's a State Park.

A better option is the Hennepin Canal trail (also a State Park), runs from Bureau Junction West to the Rock River in Colona, IL. There's also a Feeder trail that runs from the Rock River in Sterling/Rock Falls down to the Hennepin Canal near Mineral, IL. Both of these are better maintained by the State.