One implant is showing well above the gum line. Has it failed?

If the gumline simply is uneven but the implant is solid in the bone, the implant has not failed but the soft tissues may need attention.  It may be a temporary situation that resolves on its own or with minor help from the dentist and it may need much more.  If the threads of the implant are showing, it still may not be a failure yet but should be looked at by a dentist or surgeon asap.  Photos and xrays would be very helpful here.

It is excellent that you are monitoring the healing of your implants very thoroughly. An implant component that has become exposed above the gumline does not necessarily mean the implant is failing. You may just be seeing what is called a "healing abutment" which is designed to transmit through the gumline. A healing abutment would look like a smooth metal stump. If, however, you are seeing threads on the side which resemble a screw, this would be more concerning as it is probably the implant demonstrating bone loss. Either way, contact your surgeon to have a followup to ensure success. Good luck and best wishes to you. 

Gum tissue over and round implants can heal in different ways even when implants are right next to each other.  With soft tissue (gums) the variables are many:  thickness of the gum area, blood supply to same, how the implants are angled, how they are cleaned, overall body health are a few of many factors that impact healing.  The very best action a patient can take is to go see the dentist who placed the implant (s).  He or she can decide the best course of action; can correct something in a timely fashion; and/or just plain reassure you that you are on track and indeed there is no failure of the implant...this is just the way you are healing and it is normal.  Best of luck!