Let's face it - music is subjective! There is no solid, fast rule or universallly accepted defimnition of what is good, great, tasteful, bad, etc.
Opinions . . . well we all know about those. That said - he is one of my greatest influences. No question there are countless players that are more technically proficient, but U2 is not the band they are without his basslines.
Intersting discussion on Adam by Bono and Edge on an HBO special I saw last night. Edge stated he was basically a rhythm guitarist on early U2 tracks and that Adam was "lead bass." He also stated that when he was laying down the initial track to Bullet the Blue Sky, Adam and Larry joined in. The result was not what Edge intended - Adam was in a diffefent key and the "feel" was different. But when he listened back to the track, it was better than his original idea, and the song grew from there. Bono sees Adam as "edgy" (not really sure what that means, is he on edge, or like "the Edge.") Anyhow, he was very complimentary of Adam's playing, and approach to the instrument.
I agree that Adam's playing was more aggressive on earlier U2 tracks, but there are a number of great lines on recent albums.