Well they have a house style, just like Blue Note for example. I like their cover art but that's a matter of taste. I must say I like the Intakts as well. I have more problems with the SteepleChase cover art to be honest.
I'm not really fond of most of ECM's output. I tried quite some different albums lately trough Spotify that got high RYM ratings but not a lot of them actually sticked with me. A little too smooth and sometimes just a little boring for my tastes. On the other hand: they have put out some amazing music. AEOC, Roscoe Mitchell, Tomasz Stanko and Evan Parker come to mind. Mal's Free at Last and Jarrett's Survivor's Suite. Brahem is someone I always really regarded highly and there is more I just can't remember at the moment.
I'd say they have attributed a very valuable ammount of music to the whole jazz culture. Definitely understand if it's not your cup of tea, but I don't like the easy ECM bashing some people tend to do.