Inarticulate Speech of the Heart is the only Van Morrison album I own, and the reason I like it is probably also the reason you don't: - because it does not sound like Van.
Sorry, but I never liked his bluesy vocal delivery style at all, and that cloese the door to most of his albums for me. It's less off-putting on his more bouncy poppy songs like brown Eyed Girl, Come Running to Me, and Domino... and of course half of Inarticulate Speech is Instrumental, so no problem there.
I'm particularly jolted by your putdown of Celtic Swing, which I love and consider the centrepiece of the album, a track whose title describes itself perfectly. Oh well, different strokes as they say.