I hear a lot of negativity about the Spears, and while I too have not had a ton of success with them last night everything changed. I took a squad of 5 plus an Autarch for a friendly game and they dominated. To start, I held them in reserve and got a good roll for them to come in the second turn (Autarch helps with that). My opponent had a Dreadnought and scout squad in my deployment zone (we were playing capture and control). The spears flew in and since they are a big unit (big base sizes) I managed to charge both the Dreadnought and scouts together.
while I didn't destroy the dreadnought I did manage to destroy two weapons. Meanwhile, I wiped out the scouts. I survived the return attacks and while I couldn't hurt it in his assault phase since my haywire grenade failed, I simply used Withdraw and got them all out of there.
Next they assaulted a combat squad in his deployment zone and wiped them out. They got assaulted once and actually lost a guy in that but managed to withdraw and charge back. They took some shooting casualties and lost a guy charging into difficult terrain but the Autarch and Exarch survived to the end of turn 7. Their final body count was 5 scouts and 20 tactical marines.
A jetbike Autarch is a beast. He can get 6 S6 power weapon attacks on the charge. He can carry a fusion gun or a reaper launcher (either one results in dead marines). Supported by a squad of spears there is not much that can resist.
However, I don't think my experience is typical. Most of the time you will charge into a squad, devastate them and then get shot to pieces. This didn't happen too badly to me because I exploited some deployment mistakes. He wasn't able to bring all his heavy weapons to bear because I put a lot of terrain between us.
Anyway, Shining Spears are a scalpel among scalpels and really aren't for every battle. They're a hard-hitting "fun" choice. They're fast and deadly but can be very vulnerable in the shooting phase. I'm going to use them a bit more and see if I can still get some good mileage out of them.
Next game I think I am going to take Swooping Hawks, even though they suck. I used to love them back in the crazy days of 2nd edition and I want to love them again. I'll have to build a list around them.