Venom has not changed over time. All it is, is different artist's representation of the character. Each artist gives him a different look, both for their own personal preference and to give their artwork a unique feeling. But I have to agree, Venom was generally drawn alot cooler in his earlier days (I personally like Mark Bagley and Tom Lyle's version of the V-man. They both look totally awesome. Though, you can't go wrong with Todd McFarlane's version, seeing as he helped create Venom!).