This particular episode of Smallville is probably the best episode to air since reunion. This is for many reasons. For example, it takes the series back to some of it's roots. It welcomes back Lionel from a supposedly long absence, with the Luthorcorp plaza office in Metropolis. This room hasn't been in smallville for a very long time, and seeing it again brings back many memories from the smallville's past. Not to mention, Lionels conversations with Lex are always admirable.
Another pleasant return is, well uv guessed it, is Bart Allen(aka Impulse), AC(aka Aquaman) and Victor Stone(aka Cyborg). Not only does Steven Deknight reunite the former justice leaguers, he blends them in with the Smallville formula in such a unique way, that it almost feels like it is a feature length movie.
From there you get the basic story, Green Arrow forms the league, attempts to blow up 33.1, Bart gets captured, Clark saves him, and the facility is blown to kingdom com. All is good and graceful, with a good mix of stealth, action, pace and suspense. Oh, and Cyborg has some cool new upgrades true to the justice league character :).
The music is probably what makes this episode work so well. If you remember correctly, the first episode Steven Deknight directed was Agless from Season 4. This was a mediocre episode, but something felt out of place. maybe it was the music, or the acting, or the fact clark sais at the end "we didn't find you, you found us", kind of made people lose faith in the formula. But thankfully Steve Deknight redeemed himself in this Justice episode.
I had a few quivvles about Justice that made it fall short of the full 10. First of all, the far too cheesy exit of the justice league from the Ridge facility expolsion. I mean it would have been soo much cooler if say Green Arrow and Cyborg took off on Oliver's bike (rememeber from the arrow episode). Clark and Impulse should have obviously ran, and aquaman should have swam via another route. But that was soo incredibly cheesy, it nocked off 2 points from the full 10.
Secondly, another cheesy moment, not as bad as the first, but when Green Arrow sais "let's go save the world". That made me cringe. All in all, judging by the acting performances, music, direction and production values, the pros do outweigh the cons, and this is still one of the best episodes in smallville history, and maybe the 2nd best episode in season 6.
7 Out of 10...

A squashy slapstick mess posing as a comedy. Elvis Presley plays an Indian bull-riding champ who leaves the rodeo for a stay at home on his folks' desert-spread in Arizona, where government suits have just invested in the family's herd of cattle (which is in dire need of a stud). What director Peter Tewksbury is in dire need of is some narrative skills, though what he lacks in assessment he makes up for in sloppy comedic montages (his social commentary isn't exactly pointed, but Tewksbury does have a satiric bend to his outlandishness and there are some funny scenes). Despite colorful supporting turns by Katy Jurado and Joan Blondell, the general wackiness gets way out of hand, and there's too much hoopin' and hollerin' to sustain much interest. As for Elvis, he's loose and frisky throughout--and while it's nice to see him having fun on-screen, one has to wonder if he had just given up on movies at this point. This shambles of a picture has a distinct what-the-hell feel to it, and though spirits are high, the returns are mostly low. *1/2 from ****