I've picked it up, I'll be talking about it today when I record my podcast, and reviewing it somewhere down the week, perhaps even today, depending on what my schedule is like. It's been a busy, busy few weeks, and things have calmed down, but I have a review backlog, which makes finding how Sonic 4 Episode 1 fits in a little difficult.
To sum it up, it's definitely the shortest Sonic game I've ever played. Essentially, there's four worlds, three acts, a boss for each world, a little more, and the special stages.
Aside from that, I'd describe it as a step backwards for Sonic, in a few senses. It does succeed in reviving a more classic style of gameplay, but at the same time, it lacks so many of the improvements found in even Sonic 2, let alone Sonic 3 and Knuckles. Beyond that, stage design feels solid in most cases, and although it may be nostalgia talking, while these new stages don't have the same amount of character as prior Sonic stages reached, they do convey some of the same feelings. The homing attack is a miss for me. Rather than even have it, we'd be better off with Sonic capable of a light air-dash-style boost, like how the homing attack works when there's no target around. In those cases, it's a very light boost of forward momentum that feels natural to someone like me, who enjoyed the shield power-ups in Sonic 3 and Knuckles.
I don't want to get into too much more detail, so I'll be brief and say that I did feel a bit cheapened by the fact that stage design was too heavily influenced by Sonic and Sonic 2 stages, as was boss design. Too much of a rehash for me. That's it for now, if I say much more, I'd practically be writing my review, which I'm not quite ready for.