nothing they've done has been experimental.
I'd disagree with saying nothing they've done is experimental. It depends on how you use that word. Experimental FOR Weezer? Yes, they have done some things that are definitely out of the ordinary from what you would expect. In general, maybe not. Although Rivers song Greatest Man may be the only one I know of in modern rock that uses a classical "movement" structure... sooo maybe that counts?
In any case, I think the next album would be cool if they tried something... vastly different from the modern pop/rock sound. Who needs more of that? There's enough out there. I'd like to hear them try something truly different. If not in general, then at least for Weezer. You can get lost in the fluff if you aim to sound like mainstream pop.