Very nice work.
Ok, if You want suggestions, here are my 5 cents - that's how
I would do certain things, so You don't
have to follow it - just a suggestion. (not in order of importance, but rather "from tail to nose")
1) (
very minor one) - if the two nearby lines (that aren't totally vertical or horizontal) are parallell to each other I prefer to make their "pixel steps" on the same heigth/length;
2) IMHO there's too much black in some places - I'd drop it for dark grey at the wingtips and tips of horizontal stabilizer for example. Basically black is for contours/sharp ends. Also in some places too many black lines met, creating black bubble - SB/FD style allows for certain practical "modification" in such cases;
Btw. it looks like if You were using two "black colors", albeit quite randomly
3) I'd make bomb bay outlined in black rather than grey;
4) Defining the shape of engine nacelles - I'd make it by darker shade along their bottom edge (getting wider towards the widest part, but narrow near the leading edge).
5) Wheels here aren't actually circles but eggs (they have different height and width), also I'd make that metal parts in the centre mostly in dark greys, not black
6) Also, on the frames on the bomb aimers glass nose create a black blob - I'd rather try to "make an impression" that these frames are there, rather than actually place them there.
7) Seems that You have wires in two shades - I'd use two shades only when part of the wire is
actually in shade made by some element of the plane (wings etc.) - otherwise I wouldn't use different shade when the background for the wire is fuselage and different when it's "in the air".
Btw. just a small question - how many shades are You using for the "basic metal" elements? I'd say 5 is enough (with most work being comfortably done with just 4).