Next Gen: Black Ops 3 is 100% worth buying. Now, the game does have a lot of problems, which I'll go through right now.
Firstly, this is my biggest gripe with the game. It has an absurd amount of microtransactions. Now, I understand Activision has to make money somehow, but they locked some of the best weapons behind a paywall, with only a SLIM chance of getting a weapon. (I've had the game since launch, and all I have is a Crowbar.). This makes Multiplayer very pay to win.
Secondly, the campaign. Now the gameplay itself, is great. I loved the different abilities, and it'd be a great campaign... if the story even made sense. I had to look it up online, only to find out the story of the game isn't told in the cutscenes or the gameplay. It's told in that scrolling text at the beginning on each mission! Not only that, the story itself is extremely confusing.
Those are my only gripes with this version of the game. In my opinion, even getting the base game, with no DLC, is worth it. I can 100% say the same for the over 100$ of DLC.
Last Gen: Black Ops 3 on Last Gen is an entirely different beast than it's next gen counterpart. (I would rate this version of the game 2.5-3 stars.) It has a load of problems, partly stemming from the limitations of the system, but also just due to it being a bad port. Now if you ABSOLUTELY need to play Black Ops 3, and you don't have a PS4, Xbox One, or a PC, then there are a few things you're going to need to know.
Firstly, campaign is entirely gone. Now, despite what I said about it's campaign, it is a little upsetting to see it completely gutted, as it was a really fun experience.
Secondly, the game has frame rate issues. I don't have a counter on my PS3, but I can tell at times this game is going sub 15 fps. ESPECIALLY in Multiplayer.
Thirdly, the animation quality is abysmal. I don't know WHAT happened, but it's.. horrible. Guns clip through your hands, they look robotic as hell, and they look like a 10 year old's first GMOD animation. I'm not kidding when I say the animation makes this game so much worse than it is.
Fourthly, there are only 2 DLCs for this version of the game. Unlike Next Gen, where you have 13 maps, in Last Gen, you only have 3. Now that being said, the 3 maps that the game offers are some of the better maps that Next Gen has to offer. Shadows of Evil, The Giant, and Der Eisendrache. All three play semi-decently, with framedrops of 25 at the lowest. The Zombies experience is also VERY different. I can't put my finger on it, but the zombies are extremely aggressive somehow, more so than Next Gen. I'd almost say they're akin to Verruckt, but they're not that difficult.
There is one upside (or downside, depending on how you see it). The microtransactions for Black Ops 3 are non-existent. Meaning you can play without the worry of being sliced by a giant sword. Overall, it's the worst way of experiencing Black Ops 3, and really only should be played if you have no other ways of experiencing it, or you've already played Next Gen and are curious.