With wine kits, you get what you pay for.
I buy a mix of kits, from the cheap-ish $75 to the ultra premium $199 ones.
The cheaper kits are similar in quality to a "Two Buck Chuck", or a $4-5 bottle of wine. Not bad for what they are, and ok if you're not a wine snob and just want a table wine for routine dinners. These are non-complex wines, not deep in flavor, but can be very drinkable. They are ready pretty fast- about 6 weeks in total. They don't improve much with age, but the don't deteriorate all that fast either.
The really expensive kits make a wine similar to a $20/bottle or maybe even more depending on the kit. They have complex flavors and aromas, and take longer to come together. I think they boxes say they are ready in 8 weeks, but really they tend to be better with some age. I have one bottle left that I made from a kit in 2007, a tannat/merlot blend and it's been fantastic.
The expensive kits come with more juice, and little to no "concentrate". The cheaper kits come with maybe a few liters of concentrate which you dilute with water. It has a distinct "kit taste" to many, but it's not unpleasant necessarily, just more "condensed" grape flavor, if that makes sense.
The medium priced kits have a combination of the two extremes- more juice, less condensed juice, maybe some skins to ferment on, maybe some oak sawdust, but not the quality of the ultra-premium kits.
Like I said, I do a mix of them so I can have cheap everyday bottles (if you get a cheap-ish kit on sale, you can have wine at $2/bottle!), medium quality wines for dinners, and the ultra premium that is great to serve to friends who enjoy decent wine. Few of the ultra premium kits will please the ultimate wine snob, but for most who enjoy decent to good wine, those are a winner.