My mother always stewed rhubarb without sugar and froze it in blocks, adding the sugar when she defrosted it. As DH doesn't like hot sweet desserts (They're just not anything here in Germany) I never get the chance to do rhubarb crumble these days, which I would love, but wouldn't make just for me.
The only way I can use rhubarb is either as a savoury dish - served as a vegetable - or in a rhubarb cheesecake. The rhubarb goes in the bottom of a pastry base, chopped small, raw, and filled up with a sort of sweet quiche mixture, mainly using quark and eggs. Several recipes use a sachet of custard powder to set it, reducing the eggs.