I LOVE blood oranges and bemoan the short season and availability. Summer and blood oranges go hand in hand. My brother who lives in Melbourne and I will always trade barbs over who has been able to find the cheapest "bloods".
I much prefer the bloods over normal oranges (in fact very rarely will eat oranges unless it's a blood orange and then I will juice or use it in a salad much in the same way you would use grapefruit). I find that bloods aren't as sweet as normal oranges (almost a very slight bitterness). BUT then I love ruby grapefruits as well !!!
I understand the nutritional benefits are slightly higher in bloods than normal oranges. I'm not sure what the red pigmentation is called but because of this, bloods are considered to be higher in vitamin C and like many red pigment fruits and vegetables have a high anti-oxidant component. Bloods as also usually smaller in size than ordinary oranges so I'm boldly going to say perhaps they're not as high in sugar concentration than a normal orange?
I have eaten them in the past and found them slightly more bland than a Navel or Valencia. They seem to use them in soft drinks a lot so perhaps it requires more sweetening. I could see blood oranges making nice marmalade but as an eating orange they are not for me.