Doesn’t look at all bad, especially for a new transplant. The red lesions are probably ramularia leaf spot—which you also see on wild dock plants. The chlorotic/dead lesions may be something else—possibly ascochyta. I see both on rhubarb here (Kentucky 6b); named red cultivars (Canada Red, etc.) are most affected; green/blushed cultivars less so: my great-grandma’s old green-blushed rhubarb laughs at heat, humidity and fungi. The red ones usually die back severely here by summer’s end, but not before giving a good crop of stalks—and they come back reliably the next spring. Established rhubarb, provided it has good drainage (standing water and root rot are the pie plant’s direst enemies), is just about impossible to kill.
I’d remove/discard the worst affected leaves and petioles and feed the plant with something slow release to encourage establishment. Rhubarb will tolerate poor soils, but prefers a rich diet. Getting rid of dead leaves/petioles (which harbor such diseases) at the end of the season and renewing mulch will help with diseases the following season. Also, with age (and good health) the plant should become more tolerant of pathogens. Remember to feed every spring. I’ve had good luck with Espoma Holly-Tone, neem meal and fish emulsion; rotted manure and/or good compost are also great. (Rhubarb, btw, adores the cheapest fertilizer of all: human urine!) There may still be spots and a few dead leaves—that’s just life and gardening----but that won’t stop you from having a pie. 
EDIT: Forgot to say: Welcome to the forum!