I'm kinda late for the party but I was thinking a lot about platformer games so I decided to share my conclusions. I think that a good way for a platformer game to stand out is to have a strong replayability value. It seems that Ethan is lacking in that respect. Not only Ethan, most of platformers games are the same. Don't get me wrong, it doesn't mean that those games are bad, far from that! Superfrog, UnEpic, La Mulana, Escape Goat, VVVVVV, The Adventures of Shuggy (just to name a few) - I had a blast playing them but I doubt I'll come back to them earlier than in a few years (seriously!), if ever. If I'm in a mood to play a specific platformer game (arcade, puzzle, metroidvania, …) I'll simply pick a game that I've not finished yet. The market, as it was mentioned several times, is oversaturated after all. There are, however, a few platformer games that I keep coming back to:
Rogue Legacy - mostly because of its awesome heir system. There are many classes and the winning strategy is significantly different for each of them. Traits enhance the diversity even further, even though some of them are cosmetic. There are 507 upgrades you can buy for your characters + 45 pieces of equipments and 55 runes (11 unique) and and it takes a LOT of time to get them all. And they are important too! At the beginning even the first boss may smash you within seconds. Upgrade your character a bit and it will die in a few hits. To keep it short: dying is extremely original in Rogue Legacy. It doesn't really punish you. It changes the gameplay by picking a new, different heir and allowing you to upgrade your heroes. On top of that there is an elaborate New Game + mode. Every time you beat the game it becomes more and more difficult. I admit, later NG+ options are not perfectly balanced but still fun to play.
Spelunky - three words: amazing level generator. It just keeps me playing and playing. Every time the game will be different. You may be lucky and get powerful equipment early. You may be... less lucky and and die after five seconds. But what's important to emphasize: the level generator is not only random but pretty smart too! You can finish every level WITHOUT using any equipment! There is a clear (but still dangerous!) and easy to follow path between entrance and exit. But usually you don't want to reach the exit ASAP - you should take your time exploring. I love this aspect of the game because, as I said, is done intelligently - it's a pleasure to explore those areas, looking for gold, jewels and secrets.
Flashback - because of its story. The game is well known so I'll skip the details. I may also mentioned that recently
The Swapper joined this group.
In the end I'd like to mention that in most cases level editor, several game modes (just like you have in Ethan: time attack, fragment collection etc.) doesn't mean much for me. I guess that there are some people who like them but I doubt those features alone may significantly increase replayability value. So you rather need a well done New Game+ system (many NG+ were just lame!), an intelligent way to ensure gameplay diversity, a lot of freedom in building the main hero and a good story.
I hope it helps! Good luck with your next game!