Does Kane have to get 500 kills personally in 'Kirin'?
Kane himself does not have to have 500 kills; your total faction kills do. Your faction kills are represented by the white player in the leaderboard. When the white player has a score of 2000, you have made 500 kills and can confront Kirin.
Why do I have to download all the maps individually?
The maps include custom voices and music. I am keeping all parts of the campaign within the maps themselves, which means each map runs between 10-60 megabytes. Although I have uploaded some "complete versions" in huge .zip files, since I continue to edit each individual map, it becomes unwieldy to upload the whole thing over again. So, I upload each individual map to 4shared as a single zip file.
"In 'The Cave of Crystals' it seems like choosing the goon sucks compared to the reaver."
For many people, the dragoon strictly speaking is the "worse" (harder) choice. However, each choice comes with pros and cons. Poor micro of the reaver can result in not having enough scarabs to beat the mission. What is nice about the dragoon is that if you keep it alive, you can use it to kill the spore colony without taking sunken hits, and then use Jiinsh to kill the sunken without getting hit. Since I have beaten the map under the time limit for "Speed Demon" with both units, both can be used to not only beat that part of the level, but beat the level without pausing. However, since the dragoon requires better micro, I added a special achievement for people who beat the mission using it.
'Kirin' seems harder than 'Zakat'
It could be for you. It depends on how you fight Kirin, and how quickly you pick up the spell system for Zakat. I will say that I personally find it harder to get the "Duke Omnivus" statuette than to get the max gamerscore for Kirin. But your mileage may vary. If Kirin seems really hard, try a) spending more time upgrading before you go to her b) choosing the archon hero (it one-shots zergling spawns) and c) keeping Kane at full life before you confront her.
For the last mission ("Hell") how do you beat that zealot guy?
Make sure power overwhelming is not on, and then lure him over the lurker spikes. He needs to get hit by them at least three times. Make sure you are not hit by them, because they will probably kill you.
Why are some sections not voiced?
If you're talking about the end of Hell's Mission Briefing...
I really wanted to emphasize how communication with the Khala operated on a different plane of reality. As such, giving it voice at this point seemed really inappropriate. Maybe I'll change this at some point, but for now I think the lack of voice at the very end really adds to the surreal nature of the scene.