Pros: Very powerful and effective
Cons: Can leave you feeling groggy the next day
I discovered Unisom a few years ago during a prolonged bout with insomnia. I had been using various diphenhydramine-based OTC sleeping pills, which made me feel weirdly jittery if I didn't fall asleep quickly enough after taking them. Unisom SleepTabs use an entirely different drug, doxylamine succinate, and its effects are dramatically different.
The first time I tried Unisom I took one tablet. I slept very deeply for over ten hours and woke up feeling groggy and confused; I literally didn't know what day it was. This groggy, zombie-like state persisted for about six more hours.
Since then, I take half a tablet when I need to get to sleep. I still wake up feeling a bit disoriented, but that feeling passes quickly.
A couple of warnings: The first time you try Unisom, take half a tablet. If that doesn't work for you, try a whole tablet the next time. Also, don't take it at all unless you have at least eight hours (or more) to sleep. If you need to get up in six hours you'll stumble around like Night of the Living Dead for most of the next day. This medication is best if you're suffering from days of sleep deprivation and can sleep in the next morning; it's not so good if you have to get up early for work.
Also, don't confuse these with the Unisom "sleep gels" ... those use diphenhydramine.