Don't try loading old maps with this, it does not work.
This is a pretty big minus, are you planning on fixing it?
Also, why is fullscreen default if it changes the aspect ratio on widescreen monitors? I think you should enable the force aspect ratio option or find a way to scale the in-"game" viewport (resize it on window size change), but doing that second thing is really hard and I've tried it myself before.
I've had troubles with deleting entities while trying to move the screen or vice versa. Can you seperate the two functions somehow? I remember doing shift+m2 back when I did my GB mod (oh god that was a long time ago) but you could have a toggle in the toolbar or a seperate key/button all together for one of them if you want.
EDIT: Now I miss the old toolbar dynamics