Good in person, v poor online.
I've flown a few times with China Eastern from UK to China/Japan and back because their flight routes go where I need to go and their prices can be very good. Generally I have found the flights themselves and in person airport experiences to be fine although transfers in Shanghai have been an issue with long queues and a lack of resources to process transferring customers. The main problems are with the IT surrounding the company if you are not Chinese. The websites are old and super hard to navigate, the Eastern Miles membership scheme is all over the place, the app is a total waste of time, and if you need customer service support it seems the only way to get anything done is call China. So if a quality IT support network is important to you, then I would suggest using another carrier.