You will find the lens to be a quite a bit larger than the stock 18-55mm and heavier. However, you will also find that it is MUCH sharper, smoother, easier to focus (full-time manual focusing + very fast AF) and the build quality is second to none.
The 18-55mm is a great, general purpose, low cost lens that produces very acceptable images. But, if you want better quality, immediate AF and a long lasting, durable investment, the 17-40mm is a very good choice.
Good luck,
Bill