Just tried this out, and I must say the potential here is amazing. Although ground/dirt tiles don't currently look as good as structures do, the aesthetic is generally still very solid. And structures like my castle, and other housing look nothing short of beautiful. Water didn't glitch-out for me in any way, it just looked like water does otherwise. The most significant visual glitchiness was with involving lighting, with large dark areas showing up when they shouldn't, and then correcting themselves in a delayed manner -- although this wasn't too noticeable unless I was flying around with some speed.
As to be expected, framerates were not great. It was playable though for most things, like general exploration, town management stuff, etc. Fighting bosses on the other hand, proved to be a bit too much if it was normally any challenge. Also my late-game character which can fly around very quickly wasn't so do-able. Otherwise though, while noticeably a bit choppy, still fairly playable in my experience. I was mostly playing at 1080p, although lowering resolution did noticeably help the framerate. Also am I missing something, or is the Isometric option not available in-game yet? I'm only seeing the perspective view.
Never thought I'd ever play using a mod like this, but I'm glad I did. Way more people need to be trying this out. If you're planning on continuing progress here (and I hope you are), I look forward to seeing your work improved upon. Much luck to you, and incredible job so far!