Is it still possible to get the Replayer achievement in Street Fighter IV, or is the Replay Channel broken

If you haven't played any Street Fighter game since the Street Fighter 2 series, there are a few concepts to learn. The game overall feels more like Street Fighter 2 than most fighting games that have been released since then, so you will be in a familiar mindset. Using fireballs to zone your opponent to keep the distance still works, as using dragon punches to punish random jump-ins.

There are some new mechanics, though:

• Throws: throws are now used when you input light punch + light kick close to the opponent.
• Dashing: pressing forward or back twice will make your character execute a quick hop in that direction (Dan actually runs).
• Super meter: At the bottom of the screen there's a meter that's filled when you execute special attacks, when you connect with normal attacks or when you are hit by an attack. You can spend this meter when you use an EX special attack, when you cancel into a Focus attack and when you use a Super Combo.
• EX specials: most special attacks can be turned into stronger versions if you use two attack buttons for that (Ryu's fireball turn into a faster fireball that flames and knocks down the enemy). That spends 1/4 of your super meter.
• Focus attacks: executed when you input medium punch + medium kick. if you hold these buttons, your character will start a "charging" animation, and will absorb up to one attack. When you release the buttons, your character will unleash the focus attack. If you hold the buttons long enough, this attack is unblockable. You can also dash while you are holding the buttons, if you don't want to use the attack. You can cancel any attack animation when you are in the ground by pressing MP+MK during the animation. That spends half your super meter.
• Super Combos: These are moves that can only be used when your super meter is full. Most of them can be executed just after a special move, canceling its animation into the super.
• Ultra (revenge) meter: At the bottom of the screen, circling the corner of the Super meter, there's a circular meter that's filled when you are hit by attacks. Once this meter starts burning and flashing, you can spend it to execute an Ultra combo.
• Ultra combos: These are flashy and cinematic moves that can deal a lot of damage and may be used only when your Ultra meter is burning. Combos that end in Ultra combos are often the most damaging combos in the game.

There's a set of video tutorials aimed at beginners:

Ryu and Ken were nearly identical to each other in Street Fighter 2, but they became a lot different since then. Ryu is best played by using fireballs to keep the distance to the enemy and punishing their approaches, while Ken is best used in rushdown.

No, this was a feature on the console releases, but you can't switch back and forth on the PC version, as this review from IGN laments:

What's slightly disappointing about this Arcade Edition is that it doesn't give you the option to swap back to the Super rule set and 36 fighter roster. I point this out because if you download the Arcade Edition on Xbox 360 or PlayStation 3 as an upgrade to Super Street Fighter IV, you're given the ability to swap back and forth between Super and Arcade sets.