I have a Right handed Razer Death Adder. You can change the sensitivity to what you want with the Razer synapse 2.0 software you download for it. I use the 2 extra buttons as reload or melee buttons in First person shooters most times. And in MMOs like ToR or WoW the extra two mouse buttons ended up being macroed to spells 6 and 7, and the middle mouse was 5.
I think it is worth it for the first gaming mouse. But just make sure you use a mouse pad, for some reason my Death Adder twitches out sometimes all on its own and moves by itself. I think its the imperfect wood surface I am using it on though.
Is it the best mouse? I don't know, it depends how many buttons you need for the games or programs you are playing and using.
If I had...