Controls are the same as they are in any GTA game, which isn't really that great. That's its only downfall, imo, but it's definitely not the worst controls in any game ever made...they're not nearly as terrible as the Resident Evil series' controls.
However, if you have never finished the game, you've just cheated yourself out of one of the greatest gaming experiences ever. Get past the bad controls and just finish the game...you'll be glad you did.
People say it's GTA on horses, and to an extent they'd be correct, but the fact is that GTA isn't nearly as immersive as RDR...not even close. RDR is like GTA meets Max Payne in a western setting much, much bigger and much more epic than anything else Rockstar has done.