Gel was my first MAC lipstick ever and I bought it to layer under MAC lustreglass in Decorated to match my wine colored Winter Formal dress (very matchy matchy, I know). It's a frost lipstick that is described as "sheer metallic beige." When I bought Decorated at 17, I felt like it was a little too vampy for me and the MAC make-up artist suggest I try Gel underneath...and the rest is history!
The only problem I have with Gel is that I don't find it wearable on its own. I know some people do but it's just not my taste. It's just too frosty...it is a Frost after all! I pretty much only wear it when layering:
MAC Gel alone
MAC Gel alone (slightly blotted)
Stila Lip Glaze in Pomegranate alone (discontinued shade, I think)
Gel with Pomegranate on top
MAC Decorated alone
Gel with Decorated on top