Most Challenge

Street Fighter IV is probably the hardest game I've ever played. I honestly can't remember any game every making me want to throw my controller as much as this one. Or one that actually made me throw my controller so many times. I'm new to Street Fighter for the most part. Sure, I played some Street Fighter 2 Turbo, but I never owned it and arcades were never a big thing for me since that group was a few years older than I.
As you could probably say about most fighters, the game is surprisingly simple, yet shockingly complex. Out of all the fighters I've played, SFIV holds true to this more than any other. No one move is difficult to pull off alone, but discovering and applying tricks and techniques to achieve combos make the game very unique in my mind. I'm sure this is true with other Street Fighters and probably in some of the series I have never played, but I've never really played them.
My main problem with the game has been the sheer difficulty. I have heard that this was fixed with Super Street Fighter IV, but the AI is relentless to beginners. It took me over an hour to beat the game on its "Easiest" setting, and I still can't do that on Medium. 
The only other problem I found was in the execution of the online modes. When trying to play online, I was not once able to connect to a ranked quick match. The party was full every single time. I was completely clueless as to how to really play online until I tried arcade mode, and then I figured it out. While playing arcade mode with my xbox live settings on, I found it impossible to finish one single match against the AI before being met with "A NEW WARRIOR HAS ENTERED THE RING!" "Oh, cool." I thought. At first I thought the online interruption feature was pretty cool, because it reminded me of the little bit of older Street Fighter games, but after the match, which I lost, it resumed me at the beginning of the match I was on in arcade mode. I had completed the first round and was a bit irked to be pushed back to the start of the match. This time before I finished the first round "A NEW WARRIOR HAS ENTERED THE RING!" I fight. I lose. Again, my first match. Before the match even starts. "A NEW WARRIOR HAS ENTERED THE RING!" At this point I figured out that playing single player was the best way to play multiplayer and choosing to play multiplayer was the best way to no play at all. This is a horrible design, in my opinion. I don't mind being interrupted mid game for an online match or two, but I deserve to be able to advance past the first fight or two before that happens. I never got past the first match without having to quit, change the settings, and start over. Good thing it was only the first match.
In theory, that should be my biggest issue, but until I can beat the game on anything higher than Very Easy, the difficulty wins the top spot.
The trials are ridiculously hard, but test you on techniques that theoretically come in handy in real matches, although I have yet to get myself in a situation where anything past Trial 2 on normal is even possible for me.

 All in all, I've thoroughly enjoyed much of the game.  I plan on continuing to play and becoming a decent street fighter, but not without a break first. My anger and frustration levels are both a lot higher than they are for any other games and they need to cool off.

I think I'll eventually check out Super Street Fighter IV and check out how things have changed.