The Ninja is a blender and food chopper. It's a very good blender, and a fairly decent food chopper.
What the Ninja ISN'T:
IT IS NOT A JUICER. It will liquify fruits and vegetables to a drinkable state, but it does not remove the pulp. If you want true juice with no pulp (such as carrot juice and not pureed carrots), buy a juicer. Like the Vitamix, the Ninja can create "juice", but it is from the whole food and will contain pulp and possibly small chunks of food (especially hard foods like carrots).
IT IS NOT A FOOD PROCESSOR. It can be used as a food chopper, but it does not replace a food processor. It does not slice or shred, it only chops and blends. If you want to use it for chopping onion, making salsa, guacamole, pesto, sauces, etc., it should work fine. If you don't need a product to slice vegetables, or shred cheese or veggies, this may work OK as a substitute for a food processor.
IT IS NOT A VITAMIX. It may not blend quite as smoothly. It will not heat foods as it blends, so it won't make hot soup in the blender container. It doesn't have a tamper, so you may have to scrape down the sides of the blender, and you probably would want to cut whole fruit like apples into halves or quarters instead of tossing them in whole. However, the Ninja will do a pretty decent job for a lot less - probably better than most blenders. I didn't think the extra price for a Vitamix was worth it for my needs, but if you really want a Vitamix, get one.
It does come with attachments for bread dough and soft doughs (like cookie dough), but I haven't used them, so don't know how well they work.
--- Why buy a Ninja instead of a standard blender? ---
The ice crushing ability is much better than any home blender I've ever used, including my Kitchenaid that was nearly twice the price. If you want to make snow cones, slushy drinks (frozen Margaritas, Pina Coladas, etc.), or have any other need for snow-like ice, it works quite well. Do not expect it to turn out the same kind of smooth, consistent product as a commercial blender - there will probably be a few chunkier pieces left, but it does pretty well.
The multi-blade shaft works a bit better for pureeing frozen fruit than my previous blenders. All of them left a few chunky pieces of frozen fruit when I made fruit smoothies. I don't have that problem with the Ninja - it even works well on large frozen strawberries. However, be aware that a typical blender with the blades on the bottom will create a vortex that sucks the food items down from the top. The Ninja's blades work more like a food processor, which throws the food sideways against the sides of the bowl. It may not mix thick purees or very slushy drinks quite as well, and you may need to scrape the sides of the bowl.
The Ninja comes with a dough hook and dough paddles, which allow you to use it as sort of a mixer.
BOTTOM LINE: If you rarely need to turn ice into snow, blend chunks of frozen fruit, or use the food chopper ability or dough attachments, a less expensive blender is all you need. If your primary use is to make slushy bar drinks (frozen Margaritas, etc.), a commercial bar blender may give better results. If you want to frequently process whole fruit and vegetables, make nut butters, etc., and get the smoothest result, you may be better off with a Vitamix. But the Ninja is a very good choice if you want more powerful chopping ability than a blender, but don't really need (or can't afford) a Vitamix. It was perfect for my needs: frozen fruit smoothies on a daily basis, and occasionally making frozen drinks, or pureeing soups/sauces,