It's mostly anecdotal, and as I said it's second hand as it was my housemate...he pretty much said it worked as intended for a while, before eventually his emotions in every sense of the word were flat. Sure, significantly reduced manic swings, but he couldn't enjoy anything any more. It stopped his depression well enough (for a while at least), but in the long term didn't allow for any true positive emotion. He became somewhat withdrawn, and when it stopped having so much of a positive effect, he wound up depressed anyway as a result.
Also caused weight gain (albeit fluid retention), which made emotions worse.
The idea of being unable to trip pissed him off too.
I will admit I don't particularly have true reason for my opinion of lithium; I only have what my housemate has shared, and his words were enough to worry me. Even while I can't remember all the details of his time on it, I do remember the 'moral of the story' so to speak, as that's a message that sunk in.
He'd more happily 'deal with' his manic bipolar ups and downs - and the irony is that OFF lithium, he can actually obtain that emotion of happiness.
Don't take what I'm saying too strongly though. Like I said, second hand. Never been on antidepressants, and have only gone through a stage of true "depression" once (not counting minor MDMA abuse, lol), so I can't really comment as to whether it's worth it or not....but again, all I will say, is that from my second hand experience with a housemate on the stuff - not for me, ever.