Portal 2 no longer required to be installed to run TWTM! (But you still required to own it to download TWTM)
That must resolve most startup problems and crashes. - No longer "can't find background image 'materials/console/portal2_product_2.vtf" error (as required Portal 2 files are now included) - No longer "Failed to create D3D device" (or just black screen) on first start (at least for most cases when it caused by absent video settings auto-detection)
- Video settings auto-detection - no longer first start at 640x480.
Some in-game crashes should also been resolved.
If you still have crashes, verify TWTM files (Right-click on game in Steam -> Properties -> Local files -> Verify integrity of game cache)
Please post in this thread if you have issues after update.