As I type, I'm actually enjoying the benefits of peppermint essential oil. It's one of my favorites to have on hand and one of the ones I go through the quickest. It's uses are many and with proper precaution, it is one of the safest oils you can use. While it has been used for centuries to treat everything from the common cold to arthritis, it has also undergone countless scientific studies that have proven it's capabilities. Course one need not look further than the ingredients of many muscle relaxant creams to see peppermint's reach.
Plus it freshens my breath.
Scent: Just like peppermint. Though I find cheaper oil (you really need to be careful what brands you go for) tends to have a heavy metallic ring to it.
Medicinal Properties: Great for colds, peppermint oil mixed with a base oil will sooth a sore throat. In the form of capsules it's used to treat IBS and other GI issues. It can help relieve migraines and all kinds of aches and pains. While it's not a strong antibacterial oil, studies have shown when used with other oils it'll actually boost the strength of the other oils.
Flavor: Exactly as it should. Though be careful if you use it for flavoring; a couple drops goes a long way.
Warnings: Most of the warnings are about the quantity you use. As peppermint contains menthol, too much can mess with the heart, lungs, nervous system; pretty much everything. Moderation is the key to safety. And you really don't need more than a few drops at a time. You should also avoid putting it directly on the skin without diluting it in a base oil or else it will burn.
Comments: Peppermint really is, for the most part, very safe to use. If I have a sore throat I don't even bother with an oil base. I pop a couple drops in a shot glass of water and toss it back. Within seconds it soothes away the pain. Unless you're allergic to peppermint, it's an oil I would recommend for any starter kit.
Overall: Can't beat its versatility. 10 out of 10