I still feel that the resident evil (or biohazard if you will.) series are very strong and just a lotta fun.
most zombie related media just sticks to a few keyparts but doesn't expand it much. most of those movies or games don't feed a lot of the questions i have. their biggest focus is on the survivors and their choices. " will they survive? will the guy get the girl?" and stuff like that. but i feel resident evil puts more focus on the zombies, the virus and the company that started it all, wich makes it more real to me. the background story just huge! :)
just look at the birth of the virus. first the umbrella corporation created the progenitor virus, created from an ebola strain. this virus is the base of all the other virusses.
next they made the t-virus or the tyrant virus. it will reanimate dead cells (and to keep doing so it will need flesh) and in some cases cause further mutation.
then there is the t-veronica virus wich cause servere mutation in the wrong conditions, but in the right conditions it will allow the host to retain full intelligence.
next virus is the NE T-virus wich was specificly created to create tyrants (super zombies, the best known is nemesis from resident evil 2 (movie) or resident evil 3 (game)) the zombie will be very strong and a little faster. also it can be programmed to follow orders.
then there still is the G-virus, wich in the right condition also causes a tyrant like creature, with classic eye-like tumors.
there are a few more viruses created in the game but not worth mentioning in this already way to long list :P
this is one of the reasons why i love resident evil so much :D
but of course feel free/obligated :P to give your own opinions ;)