Code autocompletion is really nice in GM and permits the developers to gain a loooot of time instead of going on documentation. I'm impressed that it is not in todo list, it is one of the greatest script editor functions in GM.
fdisj ijfids pj(llelellele) - 'No errors'.
Tell me, it seems just 'a bit' screwed up. 80% of times my errors are due to syntax and LGM can't find the worse ones before compiling.
Also doc is really incomplete - You can't even know the arguments for bullet physics, box2d setup is not detailed at all ( Even less for Windows platform )
Accent support for objects - Because if you write your object/scripts/whatever names with accents, compiler will return an error.
More sound filestypes supported - Well, FLAC / WMA / etc. stuff should be interesting.
VST effects... - Should be fucking awesome for sounds effect.
... VST instruments for MID - Well, I guess I'm asking too much x)
A last - What about a better error debugger? Like, much more easier to understand.
Also I can help for french translation, do you need some help?