IMHO the problem isn't that her forehead is big, it's that her forehead sticks out because it goes up and then sharply-ish turns horizontal (top of her head), instead of sloping from one to the other gently. Foreheads generally slope backwards, the one in your drawing bulbs forwards.

Edit:

Ahh, ok, I see! Thanks for the edit, that makes a world of difference!   
I was trying to make it look like head was tilted forward though I don't think I managed to draw that very well.

Try not to get so defensive with critiques dude

Wasn't trying to be defensive, just explain why I had drawn it the way I did  I did get a little verbose there but I wanted to make sure I was totally covering all my bases.

Another update, going to call this finished after some more tweaking and maybe something of a background. I'm fairly pleased with how it came out.

Update:


Spent the remainder of my day after work tweaking things and fixing some things I realized after sleeping on it. The face was a bit too undefined and some pixel clusters near her right eye were throwing things off with the curve of her head. Also had a few other eyes look at it which was a considerable help.

Someone suggested on a PA discord server I'm in that the outlines on the bangs are taking away from things and I totally agreed. Its not where I want it just yet but its a big improvement over the glossy mess from before. I dropped her right eye down a bit and made her left one 1px less in width and also tweaked it a bit. Cutting away a lot of the details and adding some more appropriate ones really made a positive impact and I feel like I can start moving forward with the piece again.

Just a slightly unconventional tree I was messing around with, yes the I was attempting to use the mid tone as the outline for most of the other leaves... I liked the cut out look. would love to heart peoples thoughts on it!

Though this will seem pretty painful to do, I highly recommend scrapping the work you've done with your leaves and starting over. As things stand now there are large issues with lighting, banding and pillow shading; all of which are things that you seriously want to avoid. You also choose to use an outline on the leaves (a light colored one at that, for some reason) when no such outline exists on the trunk of the tree. I know that you want a sort of "cut out" look but at the moment things look pretty disjointed.

Pixel clustering really works better for leaves and trees than drawing little individualistic details and hoping that it all comes together in the end. Pixel clustering works better because you can communicate depth, light, form and the like much more easily... all the while avoiding the uncanny valley look and feel of your piece.

All in all, you're doing OK so far for where you stand. Trees can be difficult and getting them to look natural and not artificial or too rigid can be hard. I suggest looking up tutorials for pixel clustering and examples of tree's that are made with that method as well.

I know it might not really be the "look" you're after but if the look you're after is riddled with a lot of fundamental issues then sometimes its better to take a few steps back and evaluate since going forward will usually just create bad habits and more problems.

So, I always tell myself that I'm not going to edit someones work but as someone who has spent a lot of time with the sprites from the STH genesis series, I couldn't help myself. Seriously, stuff like this is my kryptonite.


So, what I tried to accomplish was to find a happy hybrid medium between your version and the classic original. Upon comparing yours and the original I felt that your highlights/hotspots and shadows were a tad exaggerated and caused the sprite to lose some of what makes Sonic's head look like his head  ( which is, essentially a big sphere with a few weird ridges above his eye socket).  I tweaked the eyes a bit (following the same method from the original) to make him appear to be looking forward as opposed to downwards and brought back some of the form and three dimensional shape that was lost from the heavy shadowing and highlighting; what helped the most was bringing down the brightness of the highlight and then uses the lightest gray shade for the hotspot.
Also, since you seemed to have tucked the left side of his head inwards, I also reduced the outside of his muzzle by one pixel just to make things look more uniform. Aside from that and unifying the light source to not look so scattered I don't think my other tweaks are all that remarkable.
The same things apply to the signs as well, made the lighting more one directional (mostly noticeable on his hand) and fiddled with the highlights so that they didn't hug his eye socket as much. As for Robotnik all I did was shorten his head a bit (they elongated his head a bit more in the modern games, before it was a simple sphere that sorta looked half melted at the bottom) and tweaked some of the shading around his mouth and chin(s).

All in all I really like what you have so far and can't wait to see where you take it all. It's kinda funny, as simple as Sonic is in terms of his design there's a lot of little complexities in there that make the sprite to be what it is. Forgive any grammar and spelling issues or if anything doesn't really make sense, I kicked into edit mode around 3am and its 4:30am now  I think it's time for bed.