Completed fangames are very rare, but GOOD fangames are even rarer. This my friends, is much more than good, it's absolutely fantastic!
There are a few bugs here and there, but it's constantly being updated with patches (the current version of the game is V.4.01a)
Even if you're not a Streets of Rage fan, this is worth downloading for the soundtrack alone. Gecko Yamori's work is outstanding and is equally matched by the other musicians that contributed. Great mix of remixes from the original games along with some brand new tracks in Yuzo Koshiro's style.
So yeah, this is one definately worth checking out. 
Note: If you're having problems with the site, mirrors are here and here.
EDIT: New patch out now!
There are a few bugs here and there, but it's constantly being updated with patches (the current version of the game is V.4.01, V.4.02 should be available within the next few days)
As a matter of fact, a 4.01a patch was released about an hour ago.
Anyways, this really is awesome. I don't feel like going into detail right now, maybe I will later, but it's clear that a lot of effort was put into this; there's even a homage to that abandoned bike stage from SoR3.
Yeah, I meant to say 4.01a. 4.02 is going to be a big upgrade and probably won't be released for another few months (think of the current version as Street Fighter 2 and 4.02 as Super Street Fighter 2).
...not Street Fighter II: Turbo or Street Fighter II: Special Championship Edition? Because SSF2 added quite a bit, considering it had four all-new characters.
Speaking of which, a Turbo thing'd be nice. Beats of Rage has one, and I was surprised at how much it spiced things up.
Other than that, saw this post and replied back at EspioKAOS' place, don't need to repeat myself.
I used the SF2 - SSF2 comparison as the update will include a few more stages (including a jetski stage - partially inspired by the surfboard stage in Shinobi 3) and enemies (one of which appears in a cutscene in the current version), along with new moves for old enemies and the option to choose between SoR2 and SoR3 versions of Axel, Blaze and Skate.
There's actually a turbo cheat of sorts in there, type SORRSPEED at the Bombergames logo when you boot the game up and the speed will be doubled.
This remake appears vastly superior to many of such things.
