In a way that is what I find appealing in his music: you think you just reached a climax, but he takes you to one even higher, and yet there is an even higher one after that. The result: you just got drained emotionally, to the point that you cant listen to anything else for quite a while. This is impressive.
I've given Wagner many a try over many a decade, and it is to be hoped those were moments when my 'ears and mind were open.' It is just not, for many reasons, to my taste. I can well believe what you said, i.e. Tristan und Isoulde
has got to be one hell of a complete wringer if you sit through the whole musico-dramatic piece in a theater! With my personal objections to Wagner, that ain't gonna happen.
The two operas I know do drain me to the point where afterwards I don't want to hear anything else, or even talk about it, are Poulenc's Dialogues des Carmélites
and Berg's Lulu.
Different strokes for different folks....