Let's look at Mariota as a prospect. I've seen most of his games, but I haven't scouted him.
Plus arm strength, can throw the ball to all areas of field without trouble. Ball arrives with zip.
Known as a cool customer in the pocket.
Makes multiple reads. Generally good at throwing the ball to the right player.
Excellent short accuracy (could be product of offense), very good intermediate accuracy, and solid deep accuracy (usually a size or speed advantage - but fast WRs are short).
Can throw accurate touch passes as needed, short and deep.
Very quick release.
Great height, looks at least 6'3.5 (listed as 6'4, but I never trust that).
High release point (actually could release it higher, given his size. The overall result is that it is high off the ground)
Great straight ahead speed, long strides (Ran for an 86 yard TD... just to prove that wasn't a fluke, he ran for another 70+ yarder in the Spring game). Good burst and agility, looks like a smooth athlete rather than exceptionally explosive.
Throwing motion reminds me of David Carr's a little too much, a little low and a little bit of push movement to it.
Very skinny. Needs to add serious bulk to be a runner in the NFL, and needs to add at least 20lbs to even be taken seriously as a passer with scrambling ability.
Too often, throws a ball that lets the defender have a shot at the pick. Usually due to relying on his arm strength.
Could go through reads quicker, although not that slow by any means.
Do not play the Robin Sherbatsky drinking game during a lengthy Mariota interview.
Footwork throwing the ball is fine, footwork setting up to throw could be a problem in the NFL.
System is not at all like NFL system.
Team is significantly better (faster) than opponents.
That sounds better than a lot of QBs that get drafted early. Certainly, he's a smarter choice than Kirk Cousins or Nick Foles. Heck, you might be able to make the case that he's better than Tannehill was - sadly, better at reading defenses (though, again, Mariota's weight is a no-go for any kind of serious NFL investment). But, yeah, he's not Stafford, Bradford, Newton, Luck, or RG3 as a prospect.
Oh yeah. He's a rFr. He certainly compares well to Luck and Bradford as rFr and to RG3 at a Fr. Not sure about Stafford or Newton, since Stafford took over midway and Newton didn't play. That's where a lot of the excitement is coming from.
In terms of tools, it's all there for Mariota to go #1. He's got more talent than Luck or Bradford, but less than RG3 or Newton. The big thing for him will be adding weight - he's not going anywhere near the top at 6'4 200 - I am assuming that he's a skinny twig at least partially because he's a rFr. He will also need to tighten up his mechanics (which will be the last step for his accuracy) and stop making the (relatively few, but too many to go #1) overly brave throws. Given the team he is on, he will need to continue to produce very efficiently. And, being a QB, he'll need to show great leadership credentials to go high in the draft. So it'll take some improvement and some time, but I think the physical package and the current level of play make Mariota as good a #1 overall pick prospect as any freshman QB.
Sarlacc, on comparing .NET to Soccer: And why not? It's a bunch of people running around in circles, feigning pain, and never scoring.