Before I start, I'd like to ask that you read my review before downvoting it instantly just because it's negative. With that said, I don't think that ESJ:GC is a terrible
game, just unfinished, and its current content is more like what you'd expect in a minor DLC or free update for the original game.
But first, let's start with the good parts. The soundtrack ranges from good at worst to amazing at best, which isn't surprising as the composer is the same as the first game's. The story and one-liners are about as quirky as in the first game, and you may or may not see that as a good thing, although for me personally the novelty of butt jokes, battlepopes and robot strippers has worn off a bit. Most of the few levels present were decently designed, with some skillfully timed jumps required at parts.
Now we get to the bad parts. One thing that I noticed right off the bat was that the ability to ground pound had been removed. Considering the original game had 4 total moves (left, right, jump, ground pound), this change is pretty significant. There's no way to get rid of missiles now, you can only jump around them, and the screen can get ridiculously cluttered with them unless if you purposely suicide after each checkpoint. I also found myself taking too long to fall at times and dying because of it, where in the original game I could have just ground pounded downwards.
Some platforming elements from the first game are either used only a few times, like the sticky walls, or not at all, like the wings. There's only one "boss", and all you have to do is avoid his attacks for around a minute. There are only a few varieties of enemies present, you could probably count them all on one hand.
These are all minor problems compared to the main issue, however: the game is just too short. I'm not particularly good at platformers, and even though I died several times, I was able to beat the entire game in slightly over an hour, getting all achievements in my first playthrough. There's no replay value at all. There is an included level editor, but this seems to be the dev's way of saying "this is all I'm doing, you finish the game". It seems to me like the dev didn't want to release these levels as free DLC for ESJ like he has in the past, but instead slapped a level designer on it and called it a new game.
I can't really complain about the price personally, since I bought this for 27 cents, but I know there are people who will want to buy it at full price. My word of advice: don't. It's basically a small level pack disguised as a sequel. Ask yourself if you think $5 is worth an hour, tops, of entertainment. You can make your money go much further than that on Steam. Of course, if you have a coupon or it's on sale, feel free to go for it if you want to burn away an hour of your time.
In conclusion, ESJ:GC has the potential to become just as good as ESJ if more (free) content is added, but as it is now, it's just a skeleton of a game that happens to have great music.
If you scrolled past all that just looking for a number, here it is: 4/10