1. Vastus medialis and vastus lateralis of the quadriceps muscle are too big from their distal halfs.
2. M. biceps femoris (or is it m. semimembranosus that you have had in mind?) - on the back of the thigh - is too "puffed" in lower part, bear in mind that its lower end is the slimmer one.
3. M. latissimus dorsi ends too soon and is too large. Bear in mind that it also attaches to lumbal and sacral vertebrae
4. The upper part of m. rectus abdominis is a lot more triangular. Follow the principle that it attaches to the 2 archs formed by ribs.
5. M. gastrocnemius is too big, the part of the foot that is lower from the knee is slimmer.
Those were the things that I noticed right away. If you need to make it look better then use this for example:
http://www.anatomyexpert.com/ When drawing contours and planning movements, take into account the places on the skeleton where different muscles attach.
btw, it looks fine all-in-all :D
hope I helped