I've missed maybe one or two Tannehill starts over the last 3 seasons, and have watched pretty much the entirety of every game that I didn't miss (have the ticket and am also Fish lover like b$).
Tannehill might be 30th in the league in throwing the deep ball. He's terrible at the long ball. Worse than 30th, actually, because guys like Edelman have also thrown better deep balls in the past year. I will give him a bit of a pass on the fact that Mike Wallace is a WR that must have the ball thrown to him in stride and at least one yard clear of any defender. Mike Wallace does not go up and get balls as a Megatron, Dez Bryant, or other elite receiver would do.
However, overall he is pretty good. He is accurate on short and medium throws and he reads defenses decently enough. He also has good speed and athleticism, and is definitely near the top of the league in QBs having the ability to gain yards on the ground.
What he also does not have is an offensive line. It would be interesting to see him have that luxury to really see whether he has enough upside on things other than the long ball to consider him to be a franchise QB.
As b$ pointed out previously he has improved every year in the league, and actually improved a lot this past season. He has had an atrocious line in 2013 and a bad line in 2014. If B. Albert comes back healthy and they pick up a very good guard the line can actually be above average, so we will see what happens in 2015.