Yeah, why would we want to have seen:
A more fleshed out character than the very one dimensional, unjustified emotionaly motived Brock we got? Why not flesh out the character and make him darker/richer than the one trick pony (yes straight out of other media I am sure) we got. There have been bad personification of characters from comics and other mediums in the past, but I still expect a world class director to give us more. Raimi felt MORE than Justified to "update" other characters storyline/characterizations (i.e. Doc Ock/MJ to name a few), so WHY NOT Brock/Venom? Perhaps it was because Venom was forced on him in SM3, or perhaps BECAUSE Venom was forced on him and he decided to show them (they want Venom.. here you go, Venom Lite and HEY.. I'll kill him too. That will show them!) Not to mention it left the franchise painted into a proverbial corner for the most part with no place to really take the story next, which ultimately cost Raimi his job.
A more epic arrival/birth of the symbiote than the highly coincidental "stealth meteror" delivery on the symbiote we got, which JUST HAPPENDED to conincide with Peter and MJ being in the exact same spot. And I know that yes (Virginia there is a Big Bad Wolf

) that comics rely on coincidence HEAVILY. But AGAIN, that does not excuse the sloppiness and unispired approach that Raimi and Co used. I would of MUCH prefered that take the approach of the Shuttle bringing the symbiote back to earth in an averted landing like the animated cartoon did. That would of been much more epic/entertaining, as well as not having been so coincidental for Peter to "obtain" the symbiote.
A more "wow" it's a sentient being from another world approach to the symbiote, while bring Connors character (IF he were a Biologist SHEESHHH RAIMI... GET A DMAN CLUE) into the mix more, which could of set up future storylines with Lizard/Connors learning from the symbiote sample he took. Exploring more IN DEPTH, the symbiotes effects on Peter, as opposed to SM3 approach basically of "WOO HOOO", this feels Grrrreeeat.
A Venom that a) knew Peter's secret identify and used it to torture Peter by threatening the ones he loved b) could evade Spider-Man's greatest weapon/defense (his Spider-Sense) c) a Venom that was stronger/faster/stronger webbing/etc. that Spider-Man/Peter, where Peter gets defeated by Venom, but not killed (yet) becuse Brock/Venom is enjoying torturing him too much. Basically again... A FLESHED OUT Brock/Venom as opposed to the one trick special we got. But heck, in SM3 Spider-Sense was a moot point anyway, a real pity considering that was the big deal with Venom, he knew Spider-Man's identify and could evade his spider-sense... a deadly combo.
Yeah, WHY would we want to see that???