Foreground video, background video, foreground audio, background audio, twisting double-meanings that take a few extra seconds to parse (& the good stuff won't slow down for you), and the occasional "I missed that entire scene because I was still laughing so hard from the previous one."

Add to all this (for those of us who don't (yet) speak Japanese), subtitles. Right now, I know enough japanese to catch bits and pieces of spoken dialog. This then gives me 1-2 audio-dialog, 1 visual-dialog, and 1-2 video tracks to attempt to follow. That's up to five raw channels. In addition, the audio channels and the subtitle channel are presenting the same information not only in different languages (with different connotations & alternate meanings), but also through different senses. You get to have fun decoding the audio signal & decrypting the video signal completely independently and allow them to meet in the middle, & play off each other...

And that's not even getting into the content coming through those channels, which can be deeper/more-multi-meaning/funnier than your average human can keep up with in realtime.

This is what makes anime head-filling. This is why anime is unique, and why it can be so nifty.

I'm almost afraid to continue my studies in Japanese. If I continue on, I will no longer need the subtitles, and will lose a channel of content.

Subtitles do not detract from anime, they enrich it.