The thing I really like about this drawing is definitely the lighting. I think you did a really great job with this drawing. There are a few mishaps I see, like with Spiderman’s proportion i.e. his hips look kinda off, and his left arm (to me anyway) looks kinda… wired, but the overall painting, texture details and background look really nice. I love the dramatic sense in the scene and I think you captured Spiderman nicely as he swings through the city. The simplistic background to is a nice touch, which makes you focus more on Spiderman.
The overall design is pretty good and the light choice is nice, but you're being beaten in the details. I'm not sure how you went about constructing the city, but the nice straight line are overshadowed by the points where it looks like you freehanded them. If the were all wavy it wouldn't be such an issue. But since the majority are clean and strait, the few wavy, irregular sections really draw attention.
For Spiderman's pose, you have good elements, but the don't necessarily fit well together. For example, the bent leg and the chest/upper abdomen look good to me but the waist/hip are seem a bit disjointed to me. The hip in particular ruins the graceful curves of the pose.
Again, overall a decent design. Just bit more attention to the details.
Lines on the left building should be straight as the rest, always do one or the other not both. His lower abdomen looks like my Mom as she got older, but I don't think spidy poped out a few kids either, but over all it's simply a awesome picture if those things were fixed. I really have not seen anything as real looking as this that draws your eyes to spiderman. I pray you can keep your way of drawing by adding the corrections as you go along. I am also glade you choosed this over the other background. You are going to be a amazing artist, so never give up, never surrender, but do listen to the other artists.