My failures were my first 2 or 3 sowings of parsnip, carrots, beetroot, spring onions, peas, french & runner beans-
then come end of June when I had almost given up so threw in loads of the above - it all took and was a raging success (also known as a glut!)
What was goo was the onions, garlic and spuds- never done these before but all were easy with no problems.
Courgettes were great, Orach (mountain spinach0 and spinach great, the kale is enormous and the purpel sprouting this spring was a complete forrest!
Genuine failures- radish, leeks (tiny), tomatoes (again

I think the apples can be classed as not a raging success since the wind blew off all but one, and there wasn't a single plum this year.
The jury is still out on the pumpkins (three potentials looking good), butternut (about 3" so not looking good) and the aubergines (healthy looking plants, no fruit yet)