16w04a was the first 1.9 snapshot I tried. About three quarters of the time, starting a game resulted in massive, overwhelming visual glitching. This occurred regardless of whether I was opening (a copy of) one of my existing 1.8 worlds or creating a brand new world in 1.9. Either way, sometimes it'd load fine, sometimes it'd be chaos.

The visual effect was more or less what can be seen starting at 36 seconds into https://www.youtube.com/watch?v=f6MuH80mlVA (I got a chaotic jumble of miscellaneous overworld fragments instead of a chaotic jumble of miscellaneous nether fragments, presumably because I wasn't in the nether at the time).

The creator of that video indicated that he had the problem when he increased render distance in Video Settings, so I tried reducing my render distance all the way down to 4 chunks, but it didn't fix the problem.

Then I experimented with other Video Settings and found that the problem DID go away once I set "Use VBOs" to "ON". It only seems to happen when VBOs are OFF.