Ultimately the last Sonic game on the Genesis is the most disappointing.
The story in a nutshell is that Dr. Robotnik is kidnapping all of the little bird creatures known as Flickies and turning them into badniks. As usual it is up to Sonic to save the day. So basically it's the same plot as the past Sonic games.
The gameplay in this game is different to that of previous Sonic games. Instead of simply running and reaching the goal Sonic now has to destroy all of the badniks to gather the Flickies in each level (consisting of two zones each) and put them inside giant rings. This is where one of the primary complaints come in. The game is incredibly repetitive in its gameplay since getting Flickies is all you really do. Like in past titles you can collect 50 rings and go into a special stage. Hidden in certain parts of the levels are either Tails or Knuckles. Collect 50 rings and find them to enter the special stage. Like in Sonic 2 you need to collect a certain amount of rings in the special stage to reach the end while also avoiding obstacles, only this time you are not in a tube but on a bridge. Luckily these stages are pretty easy to beat. You need to collect all 7 chaos emeralds to reach the final boss.
Like in past Sonic games there are a few shields and items you can obtain. The blue shield is the standard one-free-hit shield, the fire shield protects you from fire, and then there is the Homing shield. The Homing shield in this game is basically the early form of the homing attack. Do yourself a favor and try to hang on to this thing, because it is a God send to help you defeat enemies.
Now comes the game's biggest problem: The controls. The controls are incredibly slippery in this game. More often than not you are going to run into enemies because of this and it makes it harder for you to get to special stages. Not only that, but if you get hit when you have Flickies they will instantly scatter and you'll have to waste time getting them back. Getting the speed boost shoes is definitely not recommended. Trying to jump on enemies is near suicidal, so you your best option is to either roll into them or, even better, use the homing shield.
The graphics are rather decent for the Sega Genesis. Like previous Sonic games it is still bright and colorful, though some textures don't work too well. The character models do look pretty good, though. The biggest misstep in the game's presentation is in its level design. The level designs in this game come off as sloppy and often you're not sure on where to go. The isometric 3-D perspective complicates not only your navigation, but it is also frustrating trying to hit enemies. Of course the music is really good, as is standard for the series. Some tracks would actually be remixed in Sonic Adventure.
To sum things up:
-Bright and Colorful
-Sloppy level design
Unless you are an avid collector of the Sonic series it is a very hard to recommend this game. However if you really want to get this game I ultimately recommend going after the Sega Saturn version, which is said to have smoother controls and even good quality music, though the load times are a problem. It is also available on the PC, which is basically the same thing. So ultimately Sonic 3-D Blast is not the proper swan song the Genesis needed.