Why is Retriever so bad you might ask?... Lets make a list:
1) All 3 Tiers become completely and utterly useless after you get a Max Nanosuit.
2) The Killstreaks in this game aren't very great to begin with and aren't worth sacrificing a perk for.
3) The other perks you lose by using Retriever put you at a disadvantage against anyone in a gun fight that's using 3 perks that actually enhance their abilities.
Let me elaborate on #2 first. Radar is probably THE most useful Killstreak besides Max Nanosuit... and even Radar isn't THAT useful on certain maps like Chinatown that have 8 different levels that the enemy could be on. The Ceph Gunship is OKAY at best, its very "hit or miss". Sometimes it gets 0 kills for no apparent reason, other times it gets shot down right away by a Swarmer or whatever, and sometimes it may get 2-4 kills at the most which still isn't that spectacular to waste a perk on. Orbital Strike is probably my LEAST favorite Killstreak. I don't know how I get 0 kills with it sometimes when I drop it right on top of 4 enemies and they are able to literally jump out of the beam while it's cooking them. The Swarmer is OK at best, its good for taking out Pingers and Gunships, but to be effective against other players you need to have the high ground. The leaves us with EMP, which is a decent KS, but again it's nothing spectacular that would justify wasting a perk on Retriever for.
This brings me to another point that is MUCH less obvious and harder to explain, but bare with me. Picking up your dogtags right away is not ALWAYS ideal. For instance, lets say all the action is going down in the center of the map, you kill 2 people and someone else kills you before you pick up any dogtags. IF you had Retriever on, it would have gave you those 2 dogtags right away before you got killed, making those 2 kills useless. However if you DIDN'T have Retriever, you can now go collect your 2 dogtags and most likely get a couple more on your way back, now you have 2 - 3 dogtags and enough for a Radar that you wouldn't have got if you had Retriever on. Get it?
The reason why I'm making this post is my friend is raving about how awesome he is with Retriever, and I've been trying to tell him, just because you're playing well doesn't mean its because of Retriever... I doubt the Killstreak bonuses from Retriever are affecting your stats that much if AT ALL. He would be so much stronger in a gun-fight if he used all 3 perks that actually helped his gameplay, not boosting (nearly) useless Killstreaks.
Any opinions would be greatly appreciated. Help me set my friend straight pls! =P