I've studied over 7 languages in my lifetime using a bunch of different methods, and in my opinion, there is no one product that does it all. And there won't be. The best way to learn a language outside of full immersion in that country is to use as many tools as you can.
There are a lot of waste-of-time and a few waste-of-money products. Waste-of-time products are usually inexpensive, but rarely work as the primary method for learning. But they are often useful as supplements to better products. I don't really believe a product designed to help you learn a language is a waste of money unless the information it provides is wrong. Even then, finding out what's wrong (the hard way) can help you learn, albeit in an embarrassing way. Pimsleur courses are not a waste of time or money. They are among the best language learning products, and most of the time you get what you pay for.
My opinion of Pimsleur Greek I in short is that it's best in the beginning. Some people won't like it because it is so repetitive, and in all honesty, after 16 CDs, you don't walk away with much of a vocabulary. Pimsleur's comprehensive courses aren't cheap, but I really do feel they are worth it, because you may only learn a few words, but you learn so many ways in which to use those words. You pick up on the subtle differences in meaning using a small vocabulary. And that's the best way to learn.
I studied Japanese for 3 years in college, and they threw too much information at us too rapidly. My broken survival Japanese still kicks in when needed, but I had a really tough time using 3 year's worth of classes when I visited Japan. I had no confidence. It wasn't instinctual. On the other hand, I took one semester of Mandarin in college. We walked away with a tiny vocabulary, but I was amazed that I could keep up relatively well with Chinese soaps and even read subtitles at speed, years after I had stopped studying. The point is, sometimes less-is-more is true. If you visit a country, people can teach you words as you need them, but you need a foundation where the language is instinctual. You aren't thinking about grammar. You aren't even translating on the fly. The right words just come to you when you need them. That confidence is absolutely necessary.
If you are going to make an investment in learning Greek, here's what I recommend. Buy Pimsleur Greek I first. I also highly recommend How To Learn Any Language: Quickly, Easily, Inexpensively, Enjoyably and on Your Own. It will help you figure out what works for you. It's a lot of money, but before you finish Pimsleur Greek I, I'd recommend getting Rosetta Stone V2: Greek, Level 1 & 2. Rosetta is not great as a first tool if you want to have conversations. It does allow you to pick how you want to learn, especially the Homeschool version, but it tends to work better teaching you how to describe the world around you. In other words, it's great for third person descriptions, whereas Pimsleur is great for first-person interaction. You can finish the Pimsleur course in as little as a few weeks, though they sometimes take me months and months to master. But Rosetta will last you a very long time time unless you invest many hours a day. It covers a lot of ground and lots of vocabulary. I will say, learning Rosetta is a little strange and tough for some. No English. If you want to learn what a word actually means, you'll have to look it up in a Greek-English dictionary (or with cirriculum text if you get the homeschool version or purchase it separately). It's full immersion, which is great. But reading the Greek alphabet will throw some people off. You feel your way around the language. That's why a lot of peole say start with Pimsleur first, then move on to Rosetta.
Also, you will not be a good translator or interpreter on Rosetta alone. If someone asks me how to say something in Greek, I can't really do it quickly or easily. But if someone starts speaking Greek, my brain flips a switch, and I'm in Greek mode. It's disconcerting at times because it's harder to assess what you know using this method until you are speaking in the language with native speakers.
So if you are debating between Rosetta and Pimsleur, get Pimsleur first. If you make it through half of the course, you won't mind paying for Rosetta because you'll actually be getting somewhere with the language.
Of course, try to find as many Greek speakers as you can. My best friend is Greek, so I've been hearing the language for over 20 years. Try speaking what you learn in a Greek restaurant. Join a Meetup group in your city. And of course, go to Greece. Even the tiniest amount of spoken Greek will bring out that wonderful Greek hospitality.
For those of you still reading this review, if you are wondering how well Pimsleur Greek holds up in Greece, I'd say you will find that you run out of vocabulary fast just on Pimsleur. It's not so hard to follow conversations, but having one, your vocabulary will be your biggest weakness. You are learning Greek with a relatively Athenian accent, which is fine since half the country lives in and around Athens. I learned country-bumpkin hillbilly Greek first, so my accent confuses both village Greeks and Greeks from Athens. No one ever has a problem understanding me, but I'm always asked where I learned Greek because my accent shifts on a word by word basis.