It's about time we get a Sonic the Hedgehog 4.
Sonic the Hedgehog 4 was a game that Sonic fans waited a long time for and being a Sonic fan myself, I was pretty excited for this game. Sonic 4 is the first game in the original series since 1994's Sonic & Knuckles. People have thought Sonic & Knuckles was Sonic 4, but it was more like Sonic 3.5, since that and Sonic 3 were originally supposed to be one game. Sonic 4 is doing the same kind of thing, which is why "Episode 1" is in the subtitle.
You play as Sonic, who is the only playable character this time. Not even Tails or Knuckles are playable, but I would have liked seeing them playable too. As usual, your main enemy is Dr. Eggman (or Dr. Robotnik, as he was called back in the Genesis games). What's nice is seeing him return to some of his old machines, but adding new twists for the boss fights. For example, you have the classic ball and chain machine, but this time, he doesn't just move back and forth. He can also flip around and have the wrecking ball slam the ground, attempting to hit Sonic. Even Eggman in his huge robotic suit from Sonic 2 makes a reappearance here as the final boss with some new twists. After you hit him enough times, his machine goes crazy. I like that. The levels are nice and some unique ones are even thrown in. There's one level where you can ride on cards and flip cards over to gain rings or power-ups. Now isn't that just cool? There's also a level where you must finish as fast as possible, since there's a certain machine chasing you for the whole level. The homing attack is a nice addition and really helps in some areas.
Another good thing is the replay value the game has. Once you collect all the emeralds, you can become Super Sonic after collecting 50 rings in each stage by simply pressing square or triangle. You can also do time trials and attack trials and see the highest record you can get.
On the negative side, Sonic just doesn't seem quite as fast as he was in the Genesis games and the spin dash doesn't help much either. But of course, when you're Super Sonic, you're still really fast. Another thing is the gravity. Sonic stays in the air a little too long. That can get annoying when doing those time trials.
Overall, it's a great game. I wouldn't say it's as good as Sonic 3 & Knuckles, but once all the episodes are released, it'll probably be a pretty close one.