.." an average gun until you bought it and it exceeded your expectations".. that's NOT what the title of the thread asked for.. ..
it says.. " what gun were you excited/hyped about that you ended up being thrilled with once you owned it? "

but I can think of one in response to your query ..

Read about a special deal here on MGO for a complete AR-15 upper w/ BCG & CH..from a local company called Combat Armory.
I've never shot steel cased ammo in any of my (3) Ar's chambered in . 223 /5.56..,. only factory ammo or my hand loads.
As Tula & Wolf 223 was selling for about what it cost me in component cost to load my own, ( @ the time) ...I bought 1K rds,of Tula & some Wolf.
After seeing this bargain priced upper, decided it'd be a good candidate to feed that cheap ammo through.
After getting the upper, I bought a mount, rings, & scope..then attached it my Bushmaster lower.
I decided to try some of my "plinker bullets" to break it in & sight in the scope.
here's a 5 shot group from it @ 50 yds..

[IMG][/IMG]

that upper is more accurate (shoots tighter groups) than any of my other AR's.. not bad for a bargain rifle.
I decided not to feed it the steel cased ammo. Ended up selling it.