I've played too damned much Red Dead Redemption multiplayer, and felt like checking out the widespread claim that the controls and animation simply make RDR a "Grand Theft Old West." -- so I went back and played a couple hours of GTA IV multiplayer. TLDR version: a number of marginal differences add up to make GTA IV un-fun.
Anyone complaining that the RDR controls and responsiveness are identical to GTA IV, just shut your bitch mouth now. Anyone who claims the engine is the same, shut your pie hole.
The first thing I noticed is the default camera is way, way pulled back from the character, making him a smaller part of the overall scene, and coupled with Euphoria or whatever the "leaning middleware" is, making it harder to navigate obstacles. Immediately after that, I noticed F R A M E R A T E. Fraaaaaaaaaame-raaaaaaaaaaaaaaate. Oh, it's rough. I spent a good portion of time just trying to get used to predicting where my camera would be pointed during aiming. Speaking of the GTA-style auto-aim, it is improved as well; the mechanic is largely similar, but the snap-to angle of tolerance is easier to deal with, especially considering the framerate problem.
Also noticed that all of the online menus are less easy to understand exactly what's happening. There is a big 5/16 in the upper right corner, though the participating player lobby is on the left side of the screen. The game shows your current total money/XP, but not what the next level's required total or remaining-to-next-level is.
Most egregiously unthinking when considering the online "community," the randomly chosen host has complete power over what rules are in effect for the next game, including traffic density, police presence, pedestrian presence, duration, what strength level of weaponry will appear, and the real game-changer: auto-aim on/off.
There's nothing like having some spastic 12 year old decide at the last instant that he wants a 10,000 XP limit game (no time limit!) only throwing Sticky Bombs. Or suddenly find out after 5 games with auto-aim on, that the most recent host has decided for none. I prefer RDR's multiplayer which has been crafted around predetermined weapon sets, which have separate but valid win conditions.
Most strangely of all, with all the effort which must have gone into Races, there are only points awarded for first and second place. I may have seen money for third, but there's not even a consolation prize for anything past third. That makes sense in terms of authentic race podium presentation, but not for an online game. There are so many ways they could have tossed out $50 or even $10 increments for items they're already measuring and reporting, encouraging people to play more: clear a checkpoint without taking car damage, fastest lap, fastest time to clear a checkpoint, beating your previous best time during any of those, airtime during jumps, completing the race... It's like they don't want anyone to play anything other than Deathmatch.
Oddly, more people were playing it than Deathmatch. There were always full lobbies for races, which emptied out as people quick halfway through the race if it looked even a little like they might not win. I was in a three person race where the other guy was clearly going to win, and he even held up for a little bit, just to keep it seeming competitive. He was either having fun, or just wondering why I didn't quit like everyone else.