These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Americans Love Alpha 2: Alpha 2 developed a large competitive following in the US, especially on the West Coast. This is in contrast to its native Japan where it wasn't received as well, especially compared to its sequel, Alpha 3. It came to the point where it was generally accepted that the US would hands down beat Japan if they ever competed in the game, a reverse of what usually happens.
Base Breaker: Ingrid. Those who like her think she's cute and a decent fighter atop of that. Those who don't soon started screaming God-Mode Sue. The fact that she was a crossover character from a universally-hated game, and her deus ex machina storyline didn't help matters at all.
Even more so when it was confirmed that she was the reason the Street Fighter X Tekken conflict happened in the first place. Given both the fanbase's reaction to that game and the box's nature of giving prizes that are either extremely underwhelming or outright screws the winners over, she's really not helping her case any.
Common Mary Sue Traits: Ingrid has a lot, from being a precocious youngster to having the opposing force of Bison's Psycho Power.
God-Mode Sue: Ingrid possesses a version of Bison's Psycho Power (which she claims he stole from her) which functions like Rose's Soul Power but is much stronger. Rose, as powerful as her psychic abilities are, can't read Ingrid's fortune. Additionally, her powers so strong that she snaps Evil Ryu out of his trance by merely besting him in combat. She later flies off with the Buddha monument on Sagat's stage at one point. What.
Crazy Awesome: Rolento is way fixated with military jargon and utopic dreams, but hey, he can dish it out pretty well.
Charlie. The fact that's he's the Kenny of the series only seems to have bolstered his popularity among the fanbase.
Dan. He quickly became one of the series' signature characters.
Sakura. You don't get your own manga for nothing.
Karin. For a girl who has only appeared in one canonical game and two other games (Capcom Fighting Evolution and Namco X Capcom, where she's paired with Sakura no less), she has a surprisingly large fan following. She is also one of the most fan requested characters for Street Fighter IV, alongside Rainbow Mika, Elena, and Rolento.
Maki was the darkhorse of Final Fight 2, hence her appearance in the handheld versions of Alpha 3. And to pose a somewhat irrelevant question: are all the ninjas in this series darkhorses?
Rolento, who was one of the most commonly-requested characters for Super Street Fighter IV and even managed to show up in Street Fighter X Tekken years after his last appearance (Capcom vs. SNK 2), and eventually made it in Ultra Street Fighter IV.
Rainbow Mika has likely reached this status, if not after missing out on SFxT (and thus a long-awaited chance to team up with Zangief), then most certainly after being set up as the butt of a cruel joke alongside Retsu for Decapre's reveal in Ultra Street Fighter IV.
Expy: Rolento of Big Boss, of Metal Gear fame. Both are strong, charismatic men with far above average fighting skills, both lead large fighting forces, and seek to create a "Utopia" using military means. Both also obtain technology far beyond the standard of their times, namely Metal Gear and the Tanden Engine and S.I.N's "enhancement system" in Big Boss and Rolento's respective cases.
Epileptic Trees: In Rival Schools (a series with loose ties to SF), there is a character who goes by the name of Ran Hibiki. Given that Hinata learned how to fight by watching a video by Ken and Chairperson practices Saikyo, fans have been wondering if Ran is a relative of Dan's (particularly, his sister).
Fan Discontinuity: Read Ingrid's entry on Common Mary Sue Tropes above. Some people would rather pretend none of that actually happened, which is pretty easy when you consider that Ingrid doesn't make any unique or significant contributions to the storyline overall, other than being shoehorned into the storyline.
Game Breaker: Guy in the first Street Fighter Alpha due to his fast and damaging chain combos. He actually cracks a pretty bad joke in SFA3 about how he has his opponent "on a chain" in reference to this.
The crouch cancel bug in SFA3 (basically, being able to cancel longer move recoveries by crouching during a Custom Combo, which made it so that since the character using it never entered a neutral state, their opponent never got an opportunity to flip out of their combo) which made the already powerful "V-Ism" borderline broken by allowing players to kill their opponents in one long combo.
Hilarious in Hindsight: The Biblical reference to Sodom's name... which was intended as a reference to the heavy metal band Sodom.
Early in 2013, some ROM makers managed to make a Street Fighter IV hack that let you play as Rolento (using his model from Street Fighter X Tekken). In July 2013, Rolento was announced as one of the new characters to be included in the Ultra Street Fighter IV update.
Narm: Fei Long'sFunny Bruce Lee Noises being typed out and written in SFA3's Story Mode. Having him burst into "WA HOATAAAAAAAAAA!" and other screams is cool when you can hear them, not when you're reading what he says to others.
Final Bison's Final Psycho Crusher from Alpha 3. It does ridiculous amounts of damage regardless of if you block it or not. The only way to avoid it is to use a high-priority move (i.e. Shoryuken), Wall Jump, or, if you're Akuma/Evil Ryu, Ashura Senkuu it out of there. The first two require critical timing and a lot of luck.
Making matters worse is the fact that if you lose to Bison, that's it. You don't get a chance to continue and try again; it just goes straight to the bad ending.
Uncanny Valley: It may be the style, but some of the artwork done for the series can come across as pretty strange. Take a look at Dan and Zangief in the picture on this article's main page, for an example of this.