Although the initial response has been shaky, the final game looks like it could be rock-solid.
http://www.nintendoworldreport.com/preview/36266
Yoshi's New Island has a lot to prove. It's being developed by Arzest, an infant studio who has a limited roster of games under its belt (Yoshi's New Island is arguably their first proper game). Furthermore, the Arzest company is made up of key members of Artoon, a studio known for the lukewarm Yoshi's Island DS as well as the barely functional FlingSmash on Wii. Many have criticized the art style in Yoshi's New Island, noting an overall look that strays away from the crayon-inspired original and closer towards Yoshi's Story on N64. Although, as someone who takes any sequels to the beloved SNES game very seriously, I think this game still might be all right.
"This new 3DS game is a sequel, basically, to the first Yoshi’s Island. It takes place after that," says series and game producer Takashi Tezuka in an interview with IGN. While Yoshi's Island DS featured multiple babies to play as, this direct sequel seemingly focuses only on Yoshi and Baby Mario, without even Baby Luigi in sight. Perhaps the usage of "New" in the title signifies the series going back to basics in a similar manner to New Super Mario Bros.

And speaking of New Super Mario Bros., the IGN article further states that Tezuka noted "Nintendo's role on New Island, which includes himself and developers from the New Super Mario Bros. projects, is to oversee level design." Although Nintendo was likewise partially responsible for the development of Yoshi's Island DS, Nintendo seems much more up-front about making this collaboration clear; the New Island section of the latest Nintendo Direct seemed to focus specifically on this fact. At the very least, fans can be rest-assured that this game is a bit more than a small, unproven development studio taking the full reigns of the direct sequel to one of the best games ever made.
As for the gameplay, I noted in my impressions of the game at E3 that Yoshi's New Island plays very much like a proper Yoshi's Island game (which is a very good thing). It's still a collectathon of flowers and red coins, it still features enemy-swallowing and egg-throwing, and as the latest trailer showcased, you still go through rings of flowers at the end of each regular stage. Also in the impressions, I noted two new additions to the Yoshi's Island formula:
"In addition to the old stuff now, the Yoshi's New Island demo introduced two mechanics. The first is the huge throwable Yoshi egg seen in the original footage of the game. The egg itself breaks through rocks in the area to collect stones and open up pathways. It doesn't change the game excessively, but it sure is a neat addition. You can also swallow enemies like giant shy guys to make giant eggs. The other new ‘feature' I saw was a pair of binoculars that you can grab for a brief look at the entire surrounding area, which is very useful for knowing where to throw a giant egg."
The physics however, felt like they could use a bit of work as of six months ago:
"Although the game was fun and felt like Yoshi's Island, the physics do feel like they could use a bit of fine tuning. Jumping around feels a bit clunkier than older games, and egg-throwing while stationary takes twice as long as it should."
Lastly, I wanted to discuss the art style. If nothing else, the art style is curious, and seems to include both a similar 3D model style to Yoshi's Story as well as the hand-crafted pastel look of the original Yoshi's Island. For those uneasy about the new look, I encourage everyone who can to view the E3 trailer in 3D on the 3DS eShop. While New Island seems to be fully playable in 2D, the game's art style was clearly made to be enjoyed in a 3D space. Not only does it make the game look more natural and less sterile, but it gives the game a subtle-yet-effective pop brought on by a rather impressive usage of depth.
We won’t know much more about this game until we get closer to its spring 2014 release date, but one last fact I would like to re-iterate is that Nintendo is making its EAD co-development very pronounced this time around. Because of this fact alone, I have faith and confidence that the only Yoshi's New Island game they would allow themselves to release next spring is a good one.